As far as I can tell, because that is not happening.

The suggestion seems to have come from the claim that to maintain a priority queue, you have to be buying consistently. That might mean buying more than you need to ensure supply when you need it. The assumption that the excess goes into a warehouse seems to have come from someone's fevered imagination.

If there are GPUs built and not yet installed, and people who want to be using them now, money can be made getting the supply to find the demand. Most large scale companies know how to do that sort of thing. If someone has a data center and no GPUs arriving for six months, paying a few million to trade the GPUs that will exist in six months for the ones that exist now gets them an additional six months of operation, while ensuring the original buyer will have GPUs when they need them, plus a few million.