Why do we pay high wages? Because we targeted coveted players, that would earn similar wages elsewhere. The only question here is why hasn't it worked out, why players that are coveted invariably fail at United and lose value?
Before someone suggests that we shouldn't sign coveted players and focus on hungry young players, we also fail with them and outside of money our recent past shouldn't convince them to join us. It's a bit of a catch 22.
So in essence it's simple, ambitious Football clubs give big wages to coveted players and they create a structure that maximizes that investment, they don't follow the boneheaded logic of "I paid big, so now be successful!". Ambitious and successful clubs keep their players happy because they give big wages AND are successful. And finally, ambitious, well structured and successful clubs attract the best young and cheaper talents which often allows to balance the books.
PS: Spurs trapped their players, they gave them good contracts when they looked like a top club and now some of them are stuck.