Hisuian Pokémon are part of a special event right now, so that is why you are seeing then frequently. And the reason you aren't seeing Galarian Pokémon, is because they are quite rare, as there are 15 of them in the entire game. As for if Hisuian variants are more common then Galarian variants, we will have to wait and see, because this event is adding them for the first time, except for Hisuian Voltorb, who part of an event a while back that set the current one up. Hope this answers your question.