Think this is actually a key point - the fact that he isnt a guaranteed starter for us anymore, especially with Sancho coming in.
So in Pogba’s mind he probably want to go to a club where he will be (or have the personel to unleash him in a way we cant) - and in the clubs mind they probably dont want to pay above 400k /w for a guy that isnt a guaranteed starter.
Its kinda like they have outgrown eachother.
Ofcourse, the club doesnt like losing him on a free - but if he goes you still will potentially free up enough wages for two top class players that might balance the team better.
And the wage bill is something very important to United, its not all about the transfer fees.
As I think many feel , it will be great if he extends , but far from a disaster if he doesnt .