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).