It's a great question.
I think its down to coaching and lack of real leadership.
Aristotle said "The whole is greater than the sum of the parts" (Actually, he didn't, it was closer to "The system I'd something beside, and not the same, as its elements") so it's about a collective cohesive with the team and a clear direction.
Under Ole, we all know how things went: we won either with individual brilliance or swift counter attacks. There was no middle ground.
I also think the system has a part to play in it. None of our center backs are equipped to play in a back four.
I know all about that, as a Scotland fan. For 20 years we played with a back four (to my horror). We qualified for nothing. Steve Clarke switches to a back three and we qualify for Euro '20 and we're a couple wins away from World Cup qualification.
Man City and Liverpool are perfect examples of synergy and each player and each unit of their team knowing exactly what their role is and what's expected of them. At United, it's chaos personified and it has been since SAF left.
I think there's too many egos at the club. You get Bruno going into strops, Ronaldo storming down the tunnel like a child, Pogba swaggering around like he's playing a friendly, etc. These instances don't occur at Liverpool or City because they have strong managers who wouldn't tolerate it.
Everything wasn't plain sailing when SAF was in charge: Cantona doing his Bruce Lee impression, players having dust ups behind closed doors, etc) But it never spilled onto the pitch (Literally, the Cantona kick was technically outside the pitch.
) and SAF never allowed things to get toxic or a player to rock the boat. Once a player got too big for his boots, he was out.
We need a manager who will give the players an ultimatum: fall-in-line or leave.
And yeah, you're right. It's time to start backing the players, even if you don't think they should start.