When you really think about it, there's not that much difference between SM and USUM; Compared to it's remakes, it's almost the exact same game besides some extra battles and new music/locations like some kind of DLC and extra content they forgot to add in. Hell, you could say that every remake of past pokemon games did that; But unlike USUM, those games actually REMADE the game. They improved upon everything the originals did (HGSS) and even brought in some stuff from the newer installments (ORAS).

When I really thought about it, I think the real problem with USUM was it's release date.

I don't know WHY or HOW it's taking so long for Gamefreak to release Pokemon Z already since that's obviously the game that we needed.

They have the new Zygarde forms, they have the new and much better plot from what we've seen in the anime, they have the technology, so what made them think that releasing the SAME GAME with little improvements was a good idea!?