I think you've found the difficulty:
When a manufacturer sells just the receivers for common/popular rifles, it always seems as though you can get a whole rifle for very, very little more money. If you can get anything at all for the stock and/or barrel, you're almost money ahead in many cases.
My guess is (and it's only a pure guess) that the bare receivers are rarely or never discounted, or maybe just not discounted very much, from list price by the few folks who sell them. OTOH, whole rifles are frequently discounted heavily from list price. Maybe that's not it, but it's my story and I'm sticking with it!