Please look at the OP.....all the MyLeague sliders that are available are posted on page one. Tune those to your desire.
I am testing those as my season progresses. I am not simming seasons and doing that type of testing. I am far more interested in playing the game and testing game play sliders and seeing how my first off-season plays out once I get there to make any slider adjustments to the GM portion of the game.
The slider that would affect that would be Player Non-Financial Ambitions factor. I have it at 55. So it will not be only about the money. But team stability, winning, other factors other than money. So maybe he wanted to stick with your squad for reasons other then money. That puts a human emotion element into the game and contracts.
If you did not like that I would suggest you turn that back to default...or even lower than default. Other than that there is no contract/resign difficulty slider.