The most likely reason is their desire to keep their acceptance quiet until they're actually prepared for the press that the announcement would receive.
My experience with other startup folks I know is that the accelerator is not designed to be a launchpad for the company's own PR purposes. Show some restraint, built your product, gain some organic and home-grown traction and then at, or near, the conclusion of the accelerator, launch your product (demo day, for example). It is to be about the product/service, not the brand of the accelerator that earns street cred.
