There is also the fact that ideas are easy and thus cheap - good execution is hard and thus expensive. Look at grand successes that are essentially formulaic and others which take interesting concepts and squander them.

I have found some B-movies have 'moments of potential' or shockingly intelligent concepts hinted at that are quickly lost or go nowhere. One can often dig up obscure precursors to a concept - and find that there is a good reason that it remained obscure that they weren't very good even when released.