Why are Skylines less expensive than Supras of the same model?

I've seen heaps of this in the papars. A '93 R33 Skyline GTS25T OR GTS-T (one with single turbo) is ALWAYS cheaper than a '93 MkIV Supra SZ (Non-turbo at that). The Skyline, you could get around 9K whilst the Supra would be atleast 16K. Is it because Skylines are more conventional than Supras or is it because they are more popular? Or is it because R33 Skylines have a newer model after it whilst the Supra doesn't really have (apart from a cosmetic change in 1997)?