The ideal manager for the Glazers would be Jose Mourinho with no ambition: Mourinho is more or less capable of managing us to a top four finish in his sleep. However, he wants to win the title. His pride would be severely bruised if he couldn't get one over on Guardiola again. Plus, even if Pep wasn't around, for the sake of his ego he wouldn't want to leave Man Utd without winning the Premier League.
The Glazers want a manager who will finish fourth and not make too much fuss about pushing on. If you're in a 'battle' for fourth your games will get televised just as much as if you're trying to win the title, and the prize money from winning the title ain't that much bigger. From the Glazers' perspective is it worth £100m to £200m more of the club's money, much of which they could pocket themselves, just to finish a few places higher?
The squad we have is competitive enough to finish fourth, especially with Mourinho. Ergo the Glazers won't sanction anymore big spending. People are ignoring the fact we had to drop out of the top four for them to let the club spend some of its money on the team. That was the equivalent to those sides who are in the drop zone going bonkers in January to try and avoid it. All they want is top four.
Eventually Mourinho will get sick of it, as will any top manager who actually wants to win things. However, in the end I'm sure the Glazers will get a guy who is just grateful for the privilege of managing at United and can keep us top four and they'll just stick with that person.