@Lyte or any Community Support: Why do Intentional AFKs still get to keep playing this game?

Just had a game (the 2nd or 3rd today) where a player got super pissed after getting killed a couple times and decided to afk the rest of the game. Typed it out in chat, refused to help, then when he was called out on it ran into the enemy team getting blown up time after time. My question to Lyte or any other player relation person is this: When someone intentionally ruins 4 other people's gaming experiences, why do they get to keep playing the game? Why isn't this an instant and permanent ban? I'm confused by this completely, I've seen it in every division through Plat, why do players like this get to keep playing the game when they have no issues with ruining and wasting the time of others? I know I won't get an answer, but the "not as impactful " provisional games, combined with the constant afking and trolling has me at the end of my rope.