If only the majority of these sequels were truly great games that improved in every way upon the originals. Unfortunately, most of them are just rush-jobs in order to feed off of the original game's success. By the time people realise that the sequel is inferior to the original, and they regret buying it, it's too late. That's the kind of thing that Ubi Soft and EA feed off of.
Of course, that doesn't mean that there aren't good sequels...rather, they're just few and in-between.