That's not what an annulment says or means. It's formation was flawed in some way, so the basis for it to continue to be recognized as a marriage would wrong.
If annulments were only granted when there was an actual flaw in the marriage, then that would make sense, and you're right that that is the definition of an annulment. But how do you explain wealthy and influential church members like Ted Kennedy getting an annulment after so many years of marriage when it's most convenient? Are flaws in the original marriage easy to find to end one after a couple of decades?
Oh, nonsense! The abuse of the annulment process in the American Catholic Church is notorious--and was the subject of much concern on the part of the late Holy Father. It's not just that the privileged can get annulments easily. It's that anybody at all can, for nearly any reason at all, when in fact almost all the reasons come down to the same thing: The marriage didn't work out, and we want church weddings for the next go-round. If you're going to go against the words of Jesus himself on marriage and divorce, then it would be much more honest to do what the Episcopalians are doing.