You're asking the wrong question. You should ask the question of how forcing people to use their legal name instead of any old random arbitrary name they might

You're asking the wrong question. You should ask the question of how forcing people to use their legal name instead of any old random arbitrary name they might make up equals less money. And I think that's reasonably obvious. Facebook got to be as big as it is by forcing people to use their real names, so that all their acquaintances could find them easily.