It is the flip side of players holding out and demanding more money than their contract calls for because they claim they have overperformed--see Ogunleye, McCardell, etc. Teams tell players that are no longer performing to the level of their contract that they want to keep them at their current market value but that they can live without them if the player insists upon their full contract. Both sides play the game. In addition, the players know that the latter years of their contracts are unlikely to be paid without restructuring for instance in order for the Titans to exercise the last four years of McNair's contract they would have to pay him $50 mil after the 2005 season--yeah, that's happening. The no guaranteed contract thing is really misleading--large portions of the contracts are guaranteed, i.e. the signing bonus such as the $34.5 mil that Manning received up front on his new $98 mil contract.
The Art of War