Riot's community problem is so big, I'm not sure they even comprehend it
I've seen quite a few threads over the years, and with increasing frequency, about people complaining how their games are full of trolls or feeders. Which is likely increasingly true, however I'll briefly mention that a lot of these are false positives and the community has becomes increasingly salient of these behaviors over time.
The issue comes down to what's causing these players to appear so frequently. Obviously these people have always existed, but it's a particular mindset which drives players to act this way, and that shouldn't be ignored, because mindsets change. The idea that these players aren't the same players that you would've gladly played along side 3 years ago without issue is absurd. There wasn't some massive wave of trolls flooding the game, these are the existing audience of the game acting out.
So the question remains. Why are these players acting out? Well it's pretty clear, many of the players have become cynical about the game. They've just stopped caring about the actual goal of the game, because it no longer carries meaning to them. They've stopped caring about improving themselves, because they no longer view it as an achievement or bragging rights.
Now what's causing this? Well there's a few factors which can play into this for different players, but the one i'm going to focus on here, because I feel it's the most relevant, is that there's very little long term benefit. The knowledge that next season any achievement or knowledge obtained from this season is a massive contributor to this. Though, I think even more than that, the amount of champion changes is probably causing the most problems. Most people have a particular style of gameplay they enjoy in different games. I like defensive strategies in RTS games, DoT and HoT styles in action RPGs, MinionMancers in strategy RPGs, and Mobile melee brawlers in Dungeon crawlers. Yet, I'm under no misconception that these same play styles would be dreadfully boring to the majority of other players. After years of neglecting the players of a particular play style, they'll haphazardly remove them from the game.
Yet riot seems to have forgotten the concept of "target audience". Their only target seems to be a broader audience. Which means there's little time to concern yourself with the existing audience that you've already garnered. Every once in a while, you'll throw a bone to a subset of the existing audience, but that's rare enough that it seems a coincidence rather than intentional.
Riot doesn't seem to understand the beast that they're creating. A bunch of dedicated players, who are cynical about your game is worse than not having the players at all.
And none of that even starts to go into the other issues that can cause cynicism like growing authoritarian behaviors to player moderation, easily abused systems of punishment, or the constantly contradictory and/or hypocritical statements and actions.
Riot, you have a trust issue, and it's going to take at least twice as long to resolve the issue as it took to create it. And you've been creating it for years through your philosophy and practices.