I believe that the game at its core breeds toxicity.
For starters I have never played a game in my life where it was this easily accessible to report a player at the end of the game. "Report X" Almost every single game. If it wasnt right there in front of your face at the end of a match people would think twice about using it.
Second the in game chat situation. League is a team game no? Why bar players from communitcating with their teammates?
Third and most controversial is the matchmaking. I strongly believe that the matchmaking system forces loses upon a player after a win streak. This gives a player some shitty teammates who the "system" knows are going to lose. This is litterally the most tilting part of this game. I hate nothing more than when I start a game and I know its over from the first 5 mins. There is no comeback like there used to be which was what made the game so great to begin with. I would not recommend this game to anyone in its current state.