Lingard had his best season under Mourinho where we werea defensive team with counter attacking our default approach to games. In that situation, he has spaces to run into.
But under Ole, though we are still adept at counter-attacking, we are a Big team now; the teams outside top 6 sit deep and defend against us.
That is where Lingard's technical deficiencies surface. Despite his famed "movement", he moves into the useless areas i.e in the middle of 3-4 opposition players where a pass to him would amount to nothing because he doesn't have the vision or technique to turn those players and move the ball forward. So, he only does sideways or backwards pass (the same can be said of Pereira but Pereira is still more risk taking than Lingard)
He has very poor anticipation of the ball that is why a long ball to him will bounce 2,3 steps before him and he will lose the ball. That is why he cannot play the Thomas Muller or 2nd Striker role.
As a 2nd striker or no 10, he is useless due to the deficiencies I've mentioned.
The only position left for him is either the Right or Left forward - even then, he does not have specific attributes and technical capabilities to make it work. Greenwood is the default choice on the right and either Rashford or Martial on the left.
In short, he is redundant. It would do him and the club a lot of good if he moves to another top-half of the table club. But then JLingz brand would be dead. So him moving out on his own accord is too big of a dream.