Maybe its just me, but I view it as Hasbro hasn't put any major effort or plans into releasing the car MP's, rather than they can't or aren't able to.
Hasbro don't put a major effort into releasing any Masterpieces at all -- at least, not in terms of developing new moulds. Essentially all they do is adapt Tak(TOM) MPs for their market; it's more of a reactive rather than proactive approach. Ditto G1 reissues.