There is a practical reason for this. Once a position can be filled it is often filled very quickly. Getting a position can come down to who is available right now. This can even hinge on whether someone can be reached by phone that afternoon.
Also if you have a choice of interview slot, pick the earliest you can, later interviews will often get cancelled if a suitable candidate is found earlier. Companies don't want to waste time.
I got a job once that caused the next TWO DAYS of Interviews to be cancelled. This came down to being reachable by mobile phone and having access to a fax machine (this was 2001).