He's played left-wing for the majority of his entire United career. He's ineffective as a CF. Can't play RW.
But yes - he's lazy and doesn't have the intelligence to be a top class player in that position (or any position) because of this mental state. Compare that to a 37yo Ronaldo who is playing nearly every game with a sore hip, dragging this team through the mud...
You seem to find the obvious strange/baffling. Weird.
He was effective as an inside forward for LVG. Mourinho started 17/18 and 18/19 with Rashford as as starter but Martial gained a starting spot every times and then they were rotated, he was one of our best players during Mourinho's last season, including a 6 games(7goals) scoring streak under Mourinho from the spot where you said he had no influence. He was pretty effective in 19-20 as a striker and then we can agree that he was poor in terms of finishing in 20-21 which ended with a knee ligament tear.
That's why I find it weird what you deem obvious is far from obvious. Keeping in mind that we bought a striker and pushed him wide where he registered a healthy amount of goals assists despite looking awkward and lacking traits of a typical wide player.
Personally I think that he is a squad player and that's not what we purchased him for which is why moving on makes sense but I'm not going to make wild claims about his attitude or reinvent his time at United to justify it and also won't demand that United put itself in a tough spot just to validate my opinion. And I apply the same logic to Lindelof, Wan Bissaka, Shaw, Dalot, McTominay, Rashford, De Gea or Henderson.