it's because of the large number of people migrating from reddit, before that a ton of the posts you would run into (I would say at least half) were posted by lemmygrad users

R/atheism used to be an r/all sub, and I guess some people remembered that forever.

R/atheism wasn't even all bad, imo. It went over the top a lot, sometimes got ugly, but also it was cathartic and relieving for people who were trapped in super religious situations. I think it got as vehement as it did because it was often spurred on by an understandable need to vent when they couldn't in their real lives. But also it did get ugly sometimes. Shouldn't have been on r/all, like most things that end up on r/all, really.