There’s also the point at which an offer allows you to improve your side. Liverpool selling Coutinho for gazillions and buying Van Dijk and Allison probably the best example. If we sold one of White or Biss for £50M and bought Edouard and Sarr with the proceeds, we’d be a better side overall.
I believe the entire ethos of the club is to sell players for £xxm when the club is ready to promote the next hairy man child into the first team.
Not spend the profits elsewhere.