I wonder if regular models are made for mass appeal to the general public and that the quantities involved would create financial issues if those versions were unappealing. Maybe limited additions allow manufacturers to be more artistic and creative because the quantities are small & the financial risk is also small. So that allows them to really take creative risks that sometimes pay off with really great limited editions.
Another option is that the same models that you like, everybody else likes and therefore they are scarcer because of popularity.