There's a difference between shitposting and posting shit.
Shitposting is "knowingly contributing low quality, off-topic, or ill intentioned posts."
However, posting shit is just, well, y'know...shit. You post something, unironically thinking that it's good, and all you get at the end is a shit joke that nobody gives a fuck about. Ylyl/mfw/tfw are literally those kinds of shit things.
So big thanks to twoot for banning that plebbit normalnigger garbage.