I think the same is true for all social media. When you initially join, one of two things happen: 1) you find a small niche group of people who are nice and you have something in common with, the platform quickly finds its place in your mind and "Most visited" section of about:newtab OR 2) you get faced with the most generic, get-rich-quick ads/posts/rants and quickly get a sour taste for the entire platform.

Probably HN is the only place I've actually felt (1) while everything else falls into (2) after just a day or two.