first off, adujicators have their AFM and SOP to follow. They follow the law and SOP to issue rfe. not like you imagined they issue rfe by their whims.
second, if they are so dumb as to issue such rfe, the reply is straight forward: because the sponsor does not have a temporary job opening for H1B worker. They only have a permanent job for GC worker.
Again, what job opening the sponsor has is not cis business. They won't ask such baseless questions.
follow law, not your whimsical imagination.