Well, the biggest problem is not other teams wanting our best players. That is normally a good thing since it tells everyone how good they are.
The problem starts when the players wants to leave.
It undermines the team's and manager's bargaining position
since it just is good for no parties involved having a player
that doesn't want to be there and has been forced to stay by his current club.
If a big club like us ever sell players it will always be what some call "on the cheap" because there are only 2 scenarios when we ever sell.
1. Fringe players not good enough
2. Players wanting out and play for another club
We never sell the players who are good and wants to stay
which are those that cost the most.