I think the liveries (all the racing sponsorship decals and paint apps) are expensive to license. I used to collect 1:18 Diecast and some racing versions were insanely priced.
But that's the issue: the appeal is very limited--maybe these are more desirable in Japan, but I think it's safe to say the relevance is pretty lost on us.
Even I'm not collecting them...but IF the price really plummets, I might not be able resist getting at least one.