I think one of the main flaws of Reddit is that upvotes that happen on a user's front page and upvotes that come from 'within' the subreddit are treated equal (at least as far as I know).

It degrades the "does this post fit the subreddit's theme/topic?"-signal and makes the average user work against the moderation team rather than supporting them.

This was exacerbated when they started showing posts from subreddits that the user is not even subscribed to on the front page rather than just ranking posts of subscribed subreddits.

The idea that community votes will result in the best content floating to the top is flawed, because what happens is the most popular content gets upvoted and not necessarily the most insightful or pertinent. This effect is magnified as the network or communities grow and welcome more a more general audience. The most prominent commentary is often useless jokes, memes, reactions etc. Slashdot, HN, lobsters have similar flaws with different strategies to overcome them.

I'll answer - too many bots and most communities don't demand high quality comments. I still use it though - it's my only social network (although I don't think it's really a social network since I have no durable social connections with anybody there and I presume most other people don't either).