Tracking back is a coaching issue Flossy. The manager instructs the players to have certain roles in a team that include, especially for midfield players, both attacking and defending. If they aren't doing that, then that's a coaching issue. If it's a player attitude issue, then again, it's something that needs to be picked up in training and coaching.
Both Pogba and Bruno have demonstrated that, when coached right, they are world class players. That's just a fact Flos. I'm not saying Van De Beek isn't a decent player, but he's yet to set it alight at the very top level.
Man Utd have a clutch of extremely talented players, but they aren't being coached right. Ole and Ragnips aren't up to the task.
Your assessment that it's just down to ego is an oversimplification. Even Ronaldo gets hooked at that club and he's got an ego almost as big as yours