Why don't the news media report the reasons why migrants come to the UK on boats?

Mainstream news media (MSM) do not. I opted out of MSM years ago because they filter the news and misinform. Now, if I go to their sites or see a printed newspaper I only do the crosswords or look at the cartoons - NEVER, EVER read readers' comments or you'll go mad!
One podcast I enjoy is Media Storm - two young British women doing good, old-fashioned 'investigative journalism'. They cover the boat migrants stories very well indeed and never repeat dehumanising slanders against them. I use Android apps like 'Antenna Pod' (downloaded free from f-droid). It gives free access but sometimes you will hear adverts. I always use my vpn to locate myself in Japan or Cambodia i.e. a country where I cannot understand the language so that if I get ads they are incomprehensible or actually intetesting because from another culture.
I want to recommend the USA 'Cool Zone Media' podcasts too - they do a number of different podcasts. I especially enjoy 'Better Off Line', 'Cool People Who Did Cool Stuff' and 'Behind the Bastards'. Some of it discusses current affairs like political takes on migration, other programmes focus on history because this stuff is not new and we can learn lessons from reviewing what happened the last time we scapegoated 'migrants'.
All of these podcasters are creating educational, informative content and are often very funny (although sometimes the jokes are a bit off-colour so might not be everyone's cuppa tea - makes me chuckly 99% of the time).

Because that might invoke feelings of empathy & compassion for the human beings risking their lives travelling across the channel.
Or raise awareness to the criminal exploitation migrants suffer to just get a position on the boats. Or the continued exploitation they endure whilst living in the UK. Just ignore what possible reason someone would uproot their lives and travel thousands of miles illegally, I'm sure it was something small & trivial...
No no no... all our world's problems are solely caused by migrants! Certainly not the billionaires exploiting everyone pushing the narrative.
- Well said!
- Or raise awareness to the criminal exploitation migrants suffer to just get a position on the boats
  No, I've seen plenty of reporting on that. Never on the reasons they're trying to get a position in the first place though.
  
  Well then, they don't report because the reason varies from migrant to migrant. Usually there will be a line or two in the report about where and possibly why, but anything past that means they have to interview someone who isn't in a position to be interviewed.

Media gets paid billions to talk shit about migrants.
You bomb their countries and then cry about it when they come to your country.
- Media gets paid billions to talk shit about migrants.
  Eh? By whom?
  
  I am guessing that it is (1) news outlets get main income from advertisers (2) advertisers pay 'per view' (3) news outlets create 'clickbait' stories to get lots of views (4) £millions changes hands via clickbait (5) clickbait uses crude emotion to hook engagement so evoking fear, envy, anger, lust, pity etc are what 'news' is about, not in-depth nuanced reports based on facts, arguments, reason, truth and other relatively unemotional stuff. You can do 'hot takes' or you can do investigative journalism. Britain used to be global leader on high quality journalism. Now we just churn out mindless, emotionally manipulative, 'soap opera' crud.
  
  Everyone who profits off war and softer forms of imperialism. Prime examples are the defense industry, tech industry, and petroleum companies but many others benefit as well.
- Name one time Britain bombed Albania.
  
  WW2.
  My dad was RAF. From age 18, he flew from Italy, across Yugoslavia to bomb Romanian oil fields - an essential campaign in order to deny Hitler fuel/win the European war. There were very high Allied casualties. To facilitate a safe air route to Romania, Allies bombed Yugoslav territory including what is now called Albania to knock out anti-aircraft guns, intelligence/radar/communications centres, and military HQs . My dad crashed three times in his war career. (1) a few minutes after take-off, engine failure, plane written off, minor injuries but crew all survived (2) shot down over enemy territory, plane split in half, three crewmen survived including my dad - scratches but no serious injuries, everyone else died, the survivors were found by Yugoslav resistance fighters and smuggled back to Allies in Italy (3) shot down over enemy territory, plane smashed into mountainside, everyone died except my dad, trapped in burning wreckage, he crawled free, was badly burnt on hands and face (everywhere not covered by flying suit), Yugoslav resistance found him, smuggled him onto a ship, he arrived at a hospital in Cairo, Egypt where he was given plastic surgery by an expect on a visit from UK - there to train others in new techniques. Dad was invalided home. Was arrested as a suspected spy because his face no longer matched his official photograph. Was placed in prison until he was vouched for by his parents, parish priest, and former headmaster. He was all of 19 when invalided out of active duty. There were hundreds of boys with similar stories to his. Thousands who died and never even had a grave.
  British needed help from Yugoslavia (specifically from Tito's communists) in order to beat Hitler and his allies (the Balkan fascists, monarchists, nationalists, the Bulgarian fascists, the Romanian fascists). We made treaties and agreements. We cannot just conveniently forget these debts because time has passed. We British would not be here, enjoying our freedoms, without Yugoslav help. My mam's family were Jewish, if Hitler had won, she'd have died in a camp. I would never have existed. Britain owes a big debt. I owe a big debt.
  There is a much longer historic link. British have interferred in Balkan politics from at least time of Lord Byron and the Greek struggle to leave Ottoman Empire, mid-C19th. We relied on their help to beat Napoleon. We British have long historic links to these places and people. We went there, they have a right to come here. Just like the places our empire colonised are forever tied to use by history, so are the places we were once depending on for our survival. The people forced to be British citizens in the past, have a moral right to come here if they wish. The people who saved us through military alliances, have a right to our hospitality. The only Albanians I would keep out are the people who were then, and still are, our enemies - the Albanian nazis and their criminal gangs. But same goes for Americans, Indians, ANZAC, Chinese - all the allies who fought side by side with us in WW1 and WW2 - all are welcome except the scum who never helped us and never would in a future struggle.
  Educate yourself about our history!
- Poor, formerly working class, people in the UK have benefited least from the decades of foreign and economic policy that have ultimately caused the migrant crisis, and are being harmed most by it: the market for low-skilled jobs is either much more difficult or impossible, and social services are stretched past breaking. But those people are not crying, they are turning to the far-right in the (probably vain) hope for a solution because everybody else have proved themselves non-credible.
  Even though the current close-to-a-London-a-decade is simply unsustainable, it is absolutely nothing compared to the coming flood of climate refugees. The line will be drawn somewhere. The longer it goes on the stronger the response will ultimately be.
  It is a disaster but that is the reality of the situation.
  For context, the suffering migrants experience now is again nothing compared to the coming harm future migrants will experience due to climate change, and none of us can stop it, because if we don't burn those fossil fuels somebody else is going to. It isn't solvable under capitalism because the cooperation required isn't possible. Write it as an epitaph on human-kind's gravestone: "We didn't possess the wit to overcome the dopamine-driven desire for more, now."
  
  formerly working class
  Just curious why you refer to the poor people you're talking about as "formerly" working class?

Depends on the media source, if you look up a documentary you'll find the reasons stated, but if you look up article headlines it won't have the same balanced explanations (if they mention the root cause at all.)
- I'm talking about news media, to be clear. I presumed "report" would make that clear. I've edited the post title to add the word "news".

Why are they coming?

Because they can’t drive to an island
- My question is about the media.