They don't know they're asking a question that has already been answered a thousand times.
I think that hearing ASL teachers put so much emphasis on Deaf culture and what can be offending to deaf people that ASL students often want to get a feeling for how true that realy is. For example, I live in Rochester and work at RIT/NTID so I am around deaf people everyday. My mother on the other hand just took an ASL class for her job, she is a nurse in the Rochester area, and took her class at a different school. She has almost no interaction with deaf people at all. When her teacher tells her something about deaf culture she has no idea how true it is or to what degree. She is deathly afraid of using the sign for hard of hearing because she was told it is highly offensive. I could definately understand someone in a situation like that wanting to find out if something that they learned in class is true and I think once they find out that deaf people are just regular people they feel a bit sheepish for asking silly questions in the first place.
