I think it's fine to bristle at a company that just goes dark on you; that's still rude (that is, "Any communication is a gift", no, not really). A curt "Thanks, but at this time we're not going to move forward." is all it takes to not waste everyone's time.
But yeah, real feedback is never going to happen for the reasons you mention.
But yeah, real feedback is never going to happen for the reasons you mention.