Why can athletes restructure contracts : sports

I ask this question in light of recent drama surrounding athletes such as OBJ being unsatisfied with contracts they’ve been given and expecting a whole new contract with several years remaining. Maybe I’m missing something, but to me when you sign something on the dotted line you’re supposed to be good for it. The teams give guaranteed money in the contract, which can be negotiated at the time of the deal, and if they were to release the player he would be due that money. If a player thinks he’s going to play better in the future, why not sign one year deals until he thinks he’s valued appropriately? If they want the security of a long term deal, then shouldn’t they accept the fact that their value might change in the middle of the contract? What do y’all think?

Content source