>>46048137More pokémon = more sprites to draw in order to make nice animations = more time and budget to spend.
So GF opted for the easier approach and just altered the existing sprites by applying effects like rotation instead of drawing a whole new sprite, rarely actually drawing new frames.
Emerald is also guilty of this, most of the sprites have just two frames if not one, and then there's random effects so it looks like an animation.
People complain about XY idle animations but at the end of the day GF put the same amount of effort as they did back then, except with sprites it's easier to obtain a prettier result, while now it just looks like dogshit since you can't get away with these old tricks.