because you bought it used.
the new games come with a code.
EA is trying to get some of that $$$ that gamestop and places like that make flipping used games. big margins for those ngrs. they give you dick value on tradeins and then sell the used copies for only like $10 less (if you have their rewards card) than the new copies.
fuck EA though. bunch of scumbags. Ever since they locked up the exclusive NFL rights they've completely half assed their games because they have no competition. NFL 2k5 was one of the greatest football games ever made but we'll never see anotehr version because of those shady fuckers