>>32214185Why, though? If a character is just going to appear in Battle Facility, they'll need a 3D model, updated to fit the graphic of that Generation. That takes time. If a character is going to appear outside of the Battle Facility, they'll need an updated design and a role. That takes even more time.
This is time, a limited resource, being spent on, quite literally, nothing. Time that could go towards making an overall better game. Wally appeared in SM, but it added nothing. Sure, it was nice seeing him again, but no one cares. It could've been anyone. A generic NPC trainer would fit Wally's role just as well. Take Sina and Dexio. Their role was justified. Someone from another region is introducing Mega Evolution to a trainer from Alola, where Mega Evolution isn't a big thing. Even Red and Blue are justified. They needed strong trainers to be the Bosses of Battle Tree, so instead of making new characters no one cares about, like the Maison leaders, they picked two of the most beloved characters known for their strength for the job. Then there's Colress and Grimsley. Unless their roles are expanded upon in future games, they're a waste of effort.
Don't get me wrong. I like seeing older characters return. But you have choice here. Spend time bringing back characters, or make the game overall better. Between the two, I care a lot more about the latter.