There is just so much evidence in Sword & Shield, the gen 5 legendaries are in the game, regional variants and gigantamax for gen 5 pokémon, and a lot of Unova mons already have their HD models since they are in the games, whereas Sinnoh is among the least represented region and doesn't have any of these. Since gen 6, every time a region was pandered this hard, it got a remake just after.