Maybe it's just a reddit/Threadiverse thing, maybe it's stronger in political communities, but I constantly see sarcasm everywhere online, far more than anywhere else. Scroll down and you'll even see it here.
Funnily enough, in a vacuum, one might expect online forums to avoid it more, since written text can mask tone and make sarcasm unintentionally ambiguous, to the point where it's common to see people adding </s> tags to clarify. It's not rare to see arguments started when people don't recognise non-literal language.
Is it merely a habit being repeated? Is it a widespread coping mechanism for frustration? Is it simply the lowest form of wit, a simple and popular way to make fun? Is it an effective way to normalise unpopular views with the plausible deniability of just making jokes?
This is part of growing up maybe