Why people become toxic after reaching high level of skill

Hi guys I'be been playing Dota 2 from 2015(with certain breaks) and have 1.4K+ hours in this game, mostly with RU audience. After relatively so many hours I still can't understand why people who know more than you act like your old 120+ year teacher and scream when you are making something wrong?

I've just played with some guy who was spamming in chat that was saying he is a Twitch streamer blablabla and have 6,5k(russian speaking ofc lol) and was playing with us on our loved 1.2K level or something. I hope that people with same mindset as this young creature will see this post and maybe even write down their "royal" opinion on this matter. But I simply don't understand why people can behave like that.

P.S. The toxicity is why I was having such big breaks in the game. Its not even skill issues it's just there are almost always one or two morons in the game who will yell at everyone just because they exist. Yet last few games were quite enjoyable and now you can mute/report people at the same time xd