Well that'll happen when riot pushes the game to be made or lost on teamwork and coordination over individual skill. Solo players lack both of those things, but now tele ganks and 4 man gangbangs or map rotations win games more than just getting fed and stomping lane does. It's hard to solo carry now, so all those randoms feel more and more like dead weight dragging you down on games where you're doing well. On games where you're NOT doing well, YOU are the dead weight dragging your team down. Both lead to little more than anger and rage from the people you need to cooperate with to win.
Then add in that the new role select has bred a ton of spoiled bitches who feel entitled to play exactly who they want where they want every game and you have made for yourself an extremely toxic, rage-prone playerbase. I've seen entire games lost because some twat got autofilled support and decides to afk. Riot has done a lot over the last year to make the game WAY more toxic than it's ever been... while also making individual contributions and performance feel less and less meaningful. It's no wonder why so many people are burned out and leaving.