The lack of punishment for AFK/leavers is actually a joke to ragequitters
We all know that Riot doesn't punish leaving ranked matches, unless you start leaving matches with reckless abandon, like every other match. They bend over backwards to assume everyone who leaves is a situation where they need to rush to the emergency room, when truly unforeseen needs to leave a match. But how many times can one account have such an emergency?
While other competitive games will enact fairly strict punishments after just 2, sometimes 3, disconnects in a "season" (anywhere from 3 months to a year), Riot simply counts it as a "loss for the leaver, no matter the outcome of the match" (which is generally a loss for your team 4v5 anyway), and you have to type "I agree" into a laughable popup box that says you promise to not leave matches again.
It's actually a joke among the leaver community.
How do I know this? In my last game, my teammate jungler dives a turret at level 2 for a gank. He dies, we get a kill. He says "Yeah, I'm not playing this game." A teammate responds "Stay - not worth getting leaver penalty." And he says "LOL spoken like someone who never leaves matches. I leave games all the time, nothing bad has ever happened to me. Watch." He then leaves, never coming back.
Was he lying? Maybe, maybe not. Who knows what "all the time" means. But someone who gives up 3 minutes into the match strikes me as someone with a history of leaving games early.
Triggering an SR loss for 4 innocent players strikes me as far more heinous than something like verbal abuse. I can't mute the leaver and keep my SR, or at least even have a quality match that results in a loss.