Well said:

Let me again turn to Doctor Who. The casting for the role of The Doctor and Companions is a very tightly guarded secret. So much so that in many cases, it is not an open casting call, but more of a secretive, tell no one invite. In the case of the companions, the casting information does not list the show’s name or give the title “companion”. Instead a fake series name and character names are given, all to keep information from getting out. This also serves another purpose; it weeds out the egos.