It's the internet. It's full of stupid people. People think, "Oh, so this person can do this? Fine, I'll just go ahead and try this and see if I can get more views, likes, etc!"
People also do it because they get this kind of thrill when they do it. Like with the knife game song. They want to be able to do it, and if they're able to do it, then they'll feel more proud and stuff.
"You know what you are? Selfish. I've done nothing but sacrifice to get us here, and what have you sacrificed? Nothing. Zero. All you've done is boss me around - well now who's the boss? Who's the boss? It's me."