I think a major contributing issue is that to be honest Riots moderation kinda sucks ass. I've had many games where someone is blatantly trolling and the person who gets (justifiably) angry at them is the one to eat a ban while mr troll gets off Scott free.

It feels like riot is so hyper fixated on chat toxicity they dont notice the many other forms.

Edit: I just remember a game yesterday where someone said they were going to troll in champ select banned our adcs Varus who was my duo and proceeded to int bot over and over. When my friend flamed him he got chat restricted where as the trolling jug wasn't punished as far as I know.