People being toxic

I just had a game with a guy who was incredibly mad at another teammate for dying a few times, he was yelling on voice chat and just overall pissed until the other teammate left. He started saying how the game was about winning and you had to be the absolute best, and that if you die your just a loser and a liability. Why does this kind of toxicity exist? It's a PVE game not a competitive shooter or anything like that so I just don't get it