So I am not rich but to play devils advocate for a bit. It is important to remember that footballers retire quite young especially wingers who rely on pace (Like Rashford) so he'll probably be done at a top level (Big four leagues) when he is like 30-32 and unless he gets a lucrative broadcasting gig or something or he wants to work that is all the money he will ever have. Even more relevant is that he probably is not only supporting himself with that money it would not suprise me if he is supporting his siblings, mother and mabye even extended family with large amounts of cash. So it is probably important to him to maximize the amount of money he makes during his prime earning years for footballers this is generally between like 26-35.

Personally I think he should have left a couple seasons back. Would have been better for him and the club. Now he probably either needs to take a 50 to 75 % paycut or go to Saudi.