There may be other issues preventing a reissue or part 2/3 being released. DMC in texas owns the rights to DMC branding and it wouldnt surprise me that theyre demanding more money than they should be for HTs to manufacture it. They technically sued universal for bttf royalties they claimed they were owed and universal have been paying to use the cars image ever since. So the delorean has a very unique situation really and would explain why the tumbler was reissued but this isnt. Universal dont own the rights to the car, DMCH do.
As a delorean owner, i know that DMCH (as theyre known) can be very childish and dicks when it comes to this kind of thing. If they can squeeze some money out of a company, they will and if the company doesnt wanna pay the fee (which wont be small) then said company arent allowed to manufacture the product. I forget when they sued universal but iirc it was after the release of the HTs delorean.
EDIT: it appears it was 2014/2015 that DMCH started chasing universal. Sorry guys, i really dont see HT making any more of these simply because DMCH own the rights to the cars image, its badges and logo. Could also be why NECA havent released one either (did they ever release the animated version? I remember seeing it showcased).