LoL couldnt be better designed to make people rage
snowballing LoL is a game where every mistake you or your teammates make is hugely punished. every time a teammate dies your opponents gain gold, they gain xp, and they get objectives. the next time you fight those enemies they will have an advantage on you. the next kill will be easier for them and their advantage grows and grows until you don't have any chance against them.
that means every time a teammate makes a mistake you essentially become weaker. that can lead to some bad thoughts about certain people.
no escape games regularly last 40+ minutes. that is a long time to put up with trolls, afks, or terrible teammates.
for whatever reason a large percentage of players will not surrender no matter what. I have been in games where we have 2 afk and are losing 5 to 25 with inner turrets down by 20 minutes, and my team will not surrender.
troll games can be even worse. I had a game where a troll bard followed the team around all game, trying to ult us out of position so the enemy team could catch us and kill us. that game lasted 50 minutes.
there is no escape from these games. if you leave to get away from the troll or escape the torturous 3v5, there are instant leaverbuster penalties. you are held hostage until the game finally ends. this can lead to some bad thoughts.
matchmaking in the LoL matchmaking system you will lose about 50% of your games. no matter how well you play or how good you get, everyone has to lose half. this is the 'everyones a winner' system. no matter how terrible you are riot will make sure you can feel good about yourself by only playing the other very worst players. but also makes it so no one is a winner. I don't like losing half.
you will be matched up against players near your skill level every single game. that means you get no games off. there are no games to relax and mess around in. if you don't feel like trying your hardest you will get crushed. if you want to try out a new champion you will get crushed. want to duo with a friend who is new to the game? he will get beat down so badly he will never want to play with you again.
the game couldn't be better designed to make people rage. but don't you dare rage. you will get banned for 2 weeks.