Imagine you're de Bruyne. You've got a contract offer on the table. You've been the best player in the country by some distance. You've inspired your club. You're approaching your peak as a player.
Then some truculent stroppy twit pushing 30 suddenly demands and gets double the salary you've been offered.
What would you think?
Rinse and repeat for Jesus, Sterling, silva etc.
Sanchez is a fine player and would improve us. But there are 30 players in Europe who we might sign who could justifiably say 'hold on, you're paying him £500 a week. I'm as a good as him.'
The only players you can get away with paying insane wages to without the certainty of upsetting the apple cart are Messi and Neymar. Cos no one can say 'I'm better than them'.