I really have to disagree with you that it's the reason, or even the main reason.
For me Bayern, Barcelona, and City and Arsenal (to a lesser extent) have players who can receive the ball under pressure, turn their man and carry the dribble the ball towards goal, or at least keep hold of the ball. They create better angles on the ball because of this. Bayern have Thiago, Robben, Costa, Lewandowski who will all take the pass at any speed, height, angle... and control it, turn with it, or shield it. Same for Barcelona.
Meanwhile, this United team has barely one player who's great at it. So what happens is they don't want to receive the ball in tight spots, and they don't pass to each other in tight spots.
Movement alone can't carve teams open. At some point the players need to get their foot on the ball and take opposition players out of the game, and create situations where runners are encouraged to come forward. We see Silva do it all the time. Get the ball under pressure, turn, hold it, and wait for the full back to gallop forward. It was Silva's use of the ball - not Zabaleta's run - that played the biggest role in creating that chance.
Barcelona players aren't just making better runs. They're making runs that require higher levels of technique. It's no good having Mata, Memphis and Rooney running into the exact places Messi, Neymar and Suarez do, because even if they making those exact same runs, they aren't going to have the technique/composure, strength... to control the intricate passes Barcelona make constantly.
Higher levels of player are needed in order for a possession game at the level of Bayern and Barcelona.