It's also not just the amount of training they receive, but the content of the training. When you learn in Police academy that 1) everyone is armed and dangerous and 2) everyone is out to kill you, you tend to be more aggressive. And this is drilled into their skulls with the equivalent of a jackhammer. No wonder you get cops that are completely devoid of empathy, reason and humanity, but rather trigger happy assholes who will use violence for every single issue.
From what I understand the system is little bit more involved. In the Academy they technically teach you all the rules you need to abide by. But they drill the self and buddy defense imperative into you at every moment. This is so they can point at the training regimen whenever reformers make a stink.
But that's not the end of training for police officers. There's two more crucial steps. First you have to get through probation where it's really easy to fire you and your training officer basically controls that 100%. So it's a vibe check. Then they send you to continuing training seminars that propagandize police into a Hollywood Western mindset and teach them to not feel guilt or shame at killing people. Basically lowering the psychological barrier to shooting people.
Which for the record, isn't even a step the military takes. It's not hard to dehumanize someone threatening you. The only reason you'd need a class to do so, is if you're trying to dehumanize people before hand.