What determines a player's expected playing time / role within the squad?

[Swaban]

I've noticed that a few players I've tried signing are demanding to be either star player or important important player, when I only want them as squad players.

I thought it may be been based on their ability relative to other players within my squad but they are objectively worse than players I already have who play in the same positions 

[Iggy Hassan]

I always take it down one notch when I'm negotiating the contract just to avoid future upset when I rotate. 9 times out of 10 they accept it.