Why is League of Legends so cancerous?

Can't control some people's idiocy with this unfortunately. Only thing they do is pull you down and affect gameplay. I think its mostly because people want to do better to rank up, but get so tilted when someone has a bad game. I know I've snapped before.

What i tend to do most of the time is when the chat starts to go in a bad direction, i just instantly mute everyone and rely on smart pings to finish the game. Better that than standing still and arguing