Well, Riot does care about feeders and trolls.
I think the reason people don't think they do is because it's much easier to identify verbal abuse. That doesn't mean they care differently about either kind of behavior, but it does mean that one kind gets recognized and punished faster.
Rioters have said that they watch vids and monitor gameplay that way for trolls and intentional feeders. Griefing in game CAN get noticed.
But the time it takes to watch a game, and the time it takes to identify slurs and profanity in chat, is very different. One slur in chat is enough for a punishment. That takes a couple of seconds to see once the chat window is pulled up. Trolling in game is different. A Rioter will actually have to watch the vid and see if they agree, maybe even getting a second opinion. It just takes longer, period. Nothing they can do about that.
Also, if you get chat restricted, it means you are being verbally abusive. Your "I don't know how many times..." comment reveals that you haven't really learned your lesson about how to respect other people. It doesn't matter how hard they are flaming; you can't verbally abuse them. If you do, you're no better, and you are contributing to continued toxicity in the game environment.