Auditioning and actually acting on a set are two different things. When you audition, you're in a room and you don't have anything to play with and you don't have anything physically in the room. Whereas on set, you have direction, you have costumes, and you have other actors to work with. It's a completely different thing.
Doctors and scientists, being part of that two-sex culture, have done everything they can to try to force people who are in-between into one of the two clear types. Intersex people themselves have also generally wanted to fit into one of the two clear categories; most are not interested in being in a 'third' type.