Why isn't intentional feeding in ranked an instantaneous account permaban for the first offence?

Whenever I get teamed with some stupid douchebag who spends the entire game running straight up mid to feed intentionally from start to finish, (emphasis added because people seem to think I'm just whining about people who are "having a bad game") my only consolation for the wastage of my time is that the little fuckhead is going to lose his account for being such a worthless piece of shit.

Except that's not really true. Riot might give him a warning, or a slap on the wrist, or a temporary suspension. Maybe.

Which is fucking stupid. Intentionally making your entire team lose the game for no good reason (and there IS no good reason) is literally the worst thing you can do, since unlike horrendous verbal abuse it can't even be blocked. And since it's a conscious choice made over an extended period, not just a once-off thing, it can only be done by a complete asshole who is rotten to the core. Any player who does that literally doesn't deserve to play the game.

Riot, whenever you get a bunch of reports for a player who has a score of 0/18/0 in a 20-minute ranked game, 0 CS and no items except maybe Boots of Mobility, ban their entire account, immediately and permanently. There's simply no justification possible, no excuse, no reason that scum like that should be allowed to play even one more game of LoL. Yeah, they can make a new account, but they have to grind it all the way up to level 30 again to be able to ranked (how did you even let this trash play LoL for long enough to reach ranked without banning them?!) and if they have to do that enough times they'll eventually give up. Nothing else is acceptable.