>>59034573it worked for previous generations because even with advances in graphics, they were all still top-down & grid-based, so you could translate the game worlds basically 1:1 into the new styles. FRLG's maps are practically identical to RBG's, and HGSS's to GSC's. they just have new assets. even ORAS was still grid-based despite having 3D graphics, and even by that point you could see it starting to get awkward to translate the old gameboy overworlds into the new styles, it was very blocky and rigid looking.
going onto the Switch, maintaining that grid-based overworld structure that the old games were designed with, within the new style of games just isn't possible, so they would have had to redesign Sinnoh from the ground up instead of effectively just porting it into a new engine with new assets. it would have been an entirely different kind of project from the other remakes. we got spoiled with the old handheld remakes, they were really a product of their time that allowed them to be made so faithfully within the then-current game engines.