Trolls I Report Don't Get Punished

I'm honestly considering uninstalling the game from my computer. So often I get people in my games who either decide to troll/intentionally feed or simply go AFK because they don't feel like playing anymore. I understand that Riot doesn't have complete control over players' behaviors.

However, what Riot does have control over is these players' accounts. I report players like this after games. I understand that I'm supposed to receive a notification when these players are punished. The problem is that I've never received one of these notifications through the entire lifetime of my account.

It makes me angry and frustrated because it's clear that Riot simply doesn't care. I can handle being flamed and told I'm bad at the game, I can use the in-game mute feature. But when someone decides that since they lost lane they're just going to run into my lane and feed my lane opponent, causing me to also lose lane and they don't get punished for it even though my entire team and some people on the other team report the player.

Even if for some reason the notification system is just bugged or isn't used anymore, I know these players aren't getting punished because I see repeat offenders all the time. I often get the same person in two games and both games they decide to troll or go AFK. So either they weren't punished or they weren't punished severely enough to cause the to change their behavior. They get pleasure out of ruining the game for other people but Riot is to scared to be harsh with players.

But the thing that makes me more mad than anything is that I'm forced to stay in game with a troll and waste my time, causing me to feel worse when the game is over than when the game started. This isn't what a game should do. I play games to have fun, relax, and relieve stress. But having a feeder in my game ruins it for me. However I can't leave the game or else I will be punished. It makes me so angry that I will be punished if I leave a game with a troll and I know that the troll isn't going to have anything done to him/her. It's not fair that a player who plays fairly has to be subjected to at least 20 minutes of playing a game they know they're going to lose or else they risk being punished but a troll can join a game and do literally anything he/she wants without fear of punishment because Riot doesn't care.

Please explain to me how this is fair and why Riot doesn't seem to care about trolls/AFKers in their games and why they think it's better to punish the player who didn't want to deal with the troll than the troll him/herself.