Its like saying they shouldnt have done the Ultimate comic line. Why retell a story thats been done before?
Because some people might not know the original story, or a fan might want to see a new spin on one of his favorites.
First of all, this seems to be geared to a younger audience, ones who dont know the story. The comic industry needs to bring in new, young reader to build a future on.
Second, even if it wasnt geared to younger, the Avengers played a small role in the original Gauntlet series. So it would be cool to see a series that would tell the story from a new and different perspective. It wouldnt be a rehash, it would be an expansion on the story.
If Infinity Gauntlet came out now there would be dozens of tie in books; IG Avengers, IG Silver Surfer, IG Spider-Man, IG Nova, IG Guardians of the Galaxy, etc...