Why can't we get rid of people like this?

So I was playing a game with this mid. He kept on dying to a and complained about our jungler saying he was useless and shit. He kept calling it a 4v5. All lanes but mid lane was winning. Afterwards, went into a temper tantrum and decided to split bot lane for no reason while we were teamfighting. I said he would be "useless" if he continued to split bot and die. He literally just went afk after and every once in a while, he would feed the enemy team some kills. We lost an easy game because our LB literally started crying after I told him to come mid and help.

Why can't we get rid of people like that? Like people talk about "carrying" yourself out of silver or bronze or even gold but ITS NOT POSSIBLE when you literally have deadweight people on your team just like him. You can't 1v5 unless your like srsly fed. Some bullshit