Another important factor, imo, is size. Quality on platforms like Twitter, Reddit, HN, Mastodon is inversely proportional to their size. If a platform gets big enough, regardless of its motives or polish, there will be more incentive to game it.

Platforms like HN and Mastodon are great because they are small. They cater more towards a smaller, more technical community, which it isn't worth it to game with spam or whatnot because they're small and more aware of this kind of manipulation. Smaller "gems" in bigger platforms (think a small, old subreddit) can be good for the same reason.

I guess this advocates more for the small web, which I'm all for, but there's less money in that. I wonder what could practically what incentives could make the web smaller and more useful.