I think Macross Plus and 2 got released because HG was asleep at the wheel at the time. In Australia at least the popularity of anime has had its ups and downs and both these Macross titles came out at a time when there was a new 'boom' starting.
It was the time in Australia when Manga released a heap of cool anime titles at about roughly the same time. (These titles included the two macross ones, fist of the north star, project a-ko, ninja scroll, legend of the overfiend, etc....)
Taksraven