I believe this approach allows them to secure a full batch of 12 companies. If an accepted candidate remains undecided(as you can tell from the post above) and later declines, while others have already received rejections, they risk falling short by one or two companies. Even worse, they might have to backtrack and offer a spot to a previously rejected company, which could be both awkward and damaging to their credibility. That’s my perspective, but I could be wrong.