Why can't we just fix the matchmaking in Flex queue?

Why can't I just play with the people within the same MMR level, not a game where I have a bronze 4 mid, silver 5 top lane, bronze 3 jungler and unranked bottom, and a plat 5 mid and jungle, plat 3 adc, diamond 4 top lane and a gold 2 support on the other? Shit's lame as hell, it's literally impossible to win when your team refuses to group, has 60 cs at 20 minutes and makes the same mistakes over and over whereas the other team is coordinated and knows how to play the game at a decent level.