His previous team had him for few seasons probabbly.. so that when he singed he had lower quality, that would mean lower salary.
After a season or two players that improve their skills usually ask for higer salary.
You could figure out by trying to renew the contract a player with 1/2 years left.. you would notice that he would ask for more money.
Btw..What results in +Skill points does he get on stretching ? Also what stars and age is he at ?