Nice guess its on a steady decrease since 2019 althought i wonder what happened in 2018 that caused this increase usage of that word, shit was wild back then i suppose.
It wasn't a guess, dude! I'm assuming you're not aware that the merit system was implemented in Jan. 2018?
Discussion about merits and the new system was on fire in Meta for most of 2018, and I probably used the terms "shitpost" and "shitposter" dozens if not a hundred times that year (and in 2017, too, because the problem was out of control at that point). If you want some juicy reading, go look at Meta in Jan. 2018. I think the merit system was rolled out on the 28th or the 26th of that month, and that section just exploded afterward. It was an insane time, believe me.