Why do you let troll accounts exist?

I recently got into a game in my promos, I have been on a winstreak this whole season, but it gets ruined by somebody who likes to make troll accounts and ruin ranked games. The player <Removed by Moderation> came into my game, picked zoe support, then afk farmed the game. They died in the sidelanes because they didn't care whether or not they died. They ruined the entire game. I watch streams and videos on youtube about wintraders, inters, and overly toxic players, yet they don't get banned. People get boosted, you know <Removed by Moderation> is a boosting club, yet you don't try to track any boosting or anything. The only reason this community has such a toxic reputation is because riot condones, allows, and honestly seems to support it. Streamers can literally run it down on stream without punishment, except for the small few. There is no punishment for anything, and accounts are free, so why be so careful when banning, maybe just ban people from ranked? That could solve a lot of problems with trolls. Why do toxic players have to never get in any sort of trouble. Look at <Removed by Moderation> in EUW, they would disco nunu run it down, yet it would still take months for them to get banned. This season has been the most toxic due to the ranked changes as well, if somebody doesn't get their role, what is stopping them from trolling, it is worse than before. They lose 3 lp in their main role and move on. Switch ranked back, you just supported trolling with the change, i'd rather deal with a teammate less skilled in a role, because at least they are trying.