I'm going to explain the current system and why "trolls" don't get punished.
First, allow me to fully explain the system for anyone who is confused. With how the system currently is, it takes a certain amount of reports from players to get noticed by the system. Personally, it is why I hate this system because it is possible, while unlikely, but possible to get punished without saying a single thing simply because you hit that point of notice. You however will not get punished by false reports alone again, because how this system works. Yeah, we all get false reports and the system knows that hence why those "trolls" you report don't get banned. It takes a plethora of games to even get a warning, and then even more to even get chat restricted, hence why "trolls" don't get banned as often as you think, now onto the "trolls".
I'm not going to sit here and lie to you and act like trolls don't exist in this game. There are legitmate trolls, chronic afkers, and ragers in this game, however, you need to understand that you don't get one every game, you just don't, that isn't possible, no matter then elo, I have been from every elo except Master and Challenger and can say you get a TRUE troll, afker, or rager one every ten games, if that. What you DO get however is someone who snapped at that one moment and is breaking the rules that once every once in a while. That person who afks, doesn't afk every game. That "troll" who is 0/10/0 doesn't do that every game, that rager doesn't rage every game either, still report them, but you can't expect everyone who does that once to get banned? "But why not, they are breaking the rules, it should be one and done." Ok, so then every player in the game, including you and me would be banned. Don't sit here and lie and act like you have never done something like that yourself. You have trolled, you have afked, you have raged, you have done at least of these things, and that is why you see that person doing it in your one game and not being banned.
Now onto the "trolls who feed". I want you to look through your entire league match history, if you can't, go to your lolking, now tell me, is there a single game where you haven't just fed, just sucked, just got dumpstered, tried to fix your mistake and only made it worst, if the answer is yes, then you now know why that person went 0/10 that one game, if your answer is no, I need you to stop lying. Now, when someone starts feeding, yeah, it is annoying, it is infuriating in fact, but honestly, what will harping about them do? What will saying "report XXX person, feeding" going to accomplish? What is making them feel like shit going to do besides make the next couple of minutes hell? Nothing, what it might make them do is trigger them into actually feeding or afking anyway which only makes the whole experience worst.
TL; DR Not everyone who does badly or afks does it consistently which means that they aren't trolls. Not everyone who feeds is a troll. Realize that we have all fed at sometime and they likely aren't doing it on purpose.