But yea they do tend to do so and it's kinda annoying, but... We can't really stop them from doing what they want with their games. It might jsut be becuase the new gens are in fact new as well, that they jsut don't get anything... ((which is a bad excuse kinda.))
If they did Gen 2 Alolan Forms, I'd also expect them to do some Gen 4 Alolan Forms. Especially if some of those Pokemon evolve into Gen 4 Pokemon. As MUCH as I love Kanto and Hoenn, I am also a Sinnoh boy at heart, because they really had some good Pokemon in there!