Complete sets of collectibles can actually justify a premium, just as lots deserve a discount. But the driving factor is the market/demand for the subject and the PC-FX has never been popular and not only can so many games be found for next to nothing, the price range for the premium games is so wide that if price is a factor to a buyer, then they're better off just spending the day with a shopping list buying everything.
But let's face it, $2000+ is what collectards pay for hundreds of individual games today.