Welcome to the internet.
You'll find that anywhere in any video games with some sort of open chat. So if you want to find the source of why people do the things they do or say the things they say, it's not because of the game, it's because it's in their nature, so question humanity, not the game. Regardless of what game or what company it is, they cannot control people. Riot is one of the few companies who take actions against such attitudes, but no matter what, this is a free to play game and everyone has access to it.
But don't expect feedback every time. Also, just having one encounter with the individual doesn't speak for their overall history. Unless its consistently, they will not receive a penalty from one game, also unless it's against the zero-tolerance policy, even then sometimes they can dodge the bullet and not get a penalty.
Advice, don't expect feedback. Just report and move on. No matter where you go, you'll find people like that on the internet.