Anyone who thinks that it would be weird to pay the difference in Maguire's wages when he takes a step down cannot know anyone who was actually involved in professional football, this is absolutely standard for players who are reducing their wage with a move. There are three potential outcomes in this situation, in the vast majority of cases the player will be fine with leaving but not the money they are leaving behind and so meet in the middle somewhere with the money they are 'giving up', like say 80% of cases. Then you'll have 10% of cases where the player says he's not leaving without being paid the full difference and then 10% where the player just wants out and will forego what they are 'due'. I'd actually say that one is probably less than 10%, probably closer to under 5% and think about it, it's understandable, they signed a contract, clubs expect players to honour contracts, the player therefore expects the clubs to honour contracts.
In Maguire's case we could easy be in the 10% where he's asking for his full contract, it's the biggest one he'll ever have, he doesn't actually want to leave and probably feels a little forced out. He's probably looking at this from the point of view of, if I'm leaving somewhere that I don't want to leave, I'm leaving with all my money.