So if ads are just like user posts, why would companies pay for advertising when they can just have an intern, paid in "experience and exposure", make regular posts and maintain any different aliases?
Looking at the first page of my latest comments on reddit, I have some from /r/Wichita, /r/dndmemes, /r/titanfall, /r/KSPMemes, /r/wendigoon, /r/HeyRiddleRiddle, /r/DungeonMeshi, /r/Mythbusters, /r/TheLastAirbender, /r/gurrenlagann, /r/astrophotography, /r/haibanerenmei, /r/yourlieinapril, and /r/LandOfTheLustrous. There are far more, but that's just the first page.
A few of these have fediverse equivalents, most of them don't. None of them ever see active discussion on this platform. Even the ones that do will often go weeks or months between posts. Contrast that with /r/Wichita, which let me know 6 hours in advance that a capsule returning astronauts from the space station was going to fly over us at 4:38 AM on March 12th. Being able to see that made using reddit that day absolutely worth it.
Artificial ranking. Without an API it’s much less reliable for botnets to astroturf; now they’re said “if you can’t beat em, join em” and closed the API and everything is for sale: Even the honesty of the site.