Why does riot focus more on banning leavers/afk's, than toxic players?

I honestly think that riot should be focusing more on creating a much more accepting and less toxic environment. Imagine if you went into a game as malzahar ad jungle, and your entire team didn't say a single negative thing about it. Imagine if you could pick anyone and not get bashed if you messed up. Every single player has bad games and nobody has the right to flame you for it. I am not saying that anyone looking to provide positive critisism, such as "You should practice your e management on TF to get the full potential out of your ganks" or something like that, but if it's someone who is just looking to insult you for messing up, than that is totally different. They could offer even more of an incentive for being a nicer and more accepting player.