I also know people who afk , run it down mid, or ONLY farm jungle if down 1 or 2 kills and wont play with the team at all.
these people i have never seen banned and are even honor 5.
And I know about 50 threads of people banned for intentionally afk (not full afk but move around and try and fail to trick LeaveBuster), full afk that got banned from manual review, run it down blatantly from death map, and afk jungle is basically the same as intentionally afk. Browse this board, look at each thread, you'll see more people banned for those.
If chat is mutable, and the only form of toxicity that is avoidable by other players
It is not avoidable. Team chat is not muted by default. By the time someone spew verbal toxicity, it is already too late. Mute only prevent further flame, not avoidable in the first place.
why is it so focused on over other behaviors
It is not more focused. It doesn't takes much for the IFS to judge your toxic intent when you type flame. It does takes more careful review to judge game play intent and as such can be slower to be punished than verbal toxicity. To balance it out, first and second offenses for verbal is Chat Restriction (ZT notwithstanding) while first offense for game play is 14-day and then perma. Just because verbal is more easy to discern intent doesn't mean it is more "focused" than game play. It simply means it's easier to detect and punish.
