The team looks knackered and while covid is obviously not helping, its Ole's inability to rotate and his lack of trust in his squad players which is a killer.
I think he does rotate. If you look at the stats, United have actually made more lineup changes than the average team and they have also been hit less with injuries as a result.
Source: SSN
United, Arsenal, Chelsea, and Spurs all have heavy schedules due to European competitions and also progress in cup competitions so they have all made lineup changes to compensate. Having said that, in United's case, they have been heavily reliant on certain players to perform certain roles in order to function effectively.
- Bruno, very obviously, to create chances.
- Rashford to use his pace and burn teams on the counter.
- Fred for midfield workrate and pressing off the ball.
- Pogba for creativity from deeper positions.
- McT for a more all round display in various phases of the game
When the above are tired or injured they need to compensate somehow and the players they have coming in don't quite cut it for the roles they're supposed to play. As a result, for Ole it's about rotating those key players as opposed to the full squad that is the challenge. His lack of trust in squad players is mostly justified if you look at the players who can come in and play the above roles without the team experiencing a serious drop in quality.