Why are some players so verbaly offensive?

Why are some of the LoL players so verbally offensive? Tonight I have had players 'wishing your mother dies tonight', they wish me the worse diseases they can think of, just because i lack experience with a Champion, because i get them in the game twice or whatever happens. If it isn't me, it's another player that gets similar words. It happens in almost (almost, so not every) game nowadays! Why?! Is it their testosterone? Do they think it makes them a better player? Does it make them feel better to wish someones mother dead?

I do not have the idea Riot is paying enough attention to these players. Perhaps Riot can show us how many users were banned for offensive messages?

I have learned that enemies whom are defeated and allies that perform a little less often try to make players respond with the same language they use, so they can report them and hope to get them banned. Don't fall for this and do not respond to their offensive words, ignore them. It is also possible to ignore all messages from these users. Just type /help in the game to see how.