It does not help us understand how or why it happens. We can't approach the future users. Even a top secret product has to be optimized. Perhaps it's possible to find trustworthy users or user representatives. They spend time now or later struggling with product that are not adapted to their needs.
Usability testing can reveal poor usefulness of a product.
Only user requirements analysis shows how to fix it. Some of these objections are mentioned in Deborah Mayhew's tutorial on the Usability Engineering Lifecycle presented at CHI'99 in Pittsburgh.