Because you may want to improve the picture, description, etc of a product. Not everyone can get everything perfect the first time.
There were cases were Amazon's own product pages were hijacked like that in the past...
Try browsing through your oldest Amazon orders--you may very well see something you didn't buy at those links now.
If you don't, how do you fix a listing error?
This feature exists on Amazon, Etsy, eBay, etc.