Its really not a problem. What is a problem is the way remakes are utilized. Things not being expanded on is an issue in the franchise in general outside of legends arceus. 9 gens and barely anything added to the lore of mewtwo. Same goes for the unown, ho-oh, lugia, future conflicts, etc.

Legends at least expanded on the history of sinnoh and how things within the surrounding regions are connected. But pokemon is too often one and done. They could easily return to an old region with a new story and expand on the region but they always just do a remake that slightly alters the previous lore. Johto is not held back by anything but creative liberties. All the ingredients are there they are just not as concerned with using them.

If they made a fleshed out johto story and kanto was still there nobody would ever complain. The execution is the problem, not kanto.