It's not that simple...Competitive players for example are forced to buy the games if they wanna do what they do. This move, now, in 2017, sounds really like "we want to make more money, let's make the same game but better next year". BW2 did a step forward with sequels, Gen 6 completly skip it for remakes, now after 10 years we are back to Platinum. Some fans just think that they could have simply made S/M better games and skip USUM. Marketing is marketing and money is money, true, but they could have done something more original this is certain or at least they coud have tried to look like they trust these games.
Imo, despite the marketing move, I'm happy Necrozma and all the plot in Alola will not receive the Zygarde treatment. I just hope they did not make another uncomplete game like s/m cause that would be terrible, you took the risk to create better versions of games after one year, well let them be really better versions or this will be really the worst waste of money in 10 years.
This is what frustrates me the most, it's when people like you say that not enough has changed, but when you step back and look at everything as a whole, here's where the changes outweigh the nonchanges:
Things that are new/have been hinted at but not elaborated on:
New trials/reworked trials
Four brand new characters that have had no info released about them
What appears to be Lt. Surge's gym (and the fact that an unused gym model was found in a recent datamine of SM a month ago)
Ryuki having a larger role
Kahili teaching us a Z-move at what appears to be Ten Carat Hill
Mantine Surf
The new Z-ring
Kiawe has been confirmed as a trial captain but is oddly missing from his original trial site
New areas on the map that haven't been showcased yet
The Pikachu Park which is missing from the region map
New buildings that aren't the Alola Photo Club
The Alola Photo Club
At least two BRAND NEW Pokémon
Roughly 100 Pokémon being added to the regional dex
New scenes with Hau and Hala
New scenes with Necrozma
The lack of anything Team Skull
Brand new Z-moves
Tougher opponents (as evidenced by Hau having 4 Pokémon at Paniola Town instead of 2, though this could actually indicate a newly reworked order of trials too)
New plot points (as evidenced by the starter selection event amongst other things: see above)
New forms of older Pokémon (Lycanroc and Necrozma so far)
Things that have been CONFIRMED to stay the same:
A few plot points involving Lille
The scene at Aether with Lusamine and Hau (although if it is still Nihilego to come out of the portal has NOT been confirmed)
So when taken and looked at like this, it baffles me that people can still say that we don't know enough/this game hasn't changed enough from SM, when clearly the new things revealed and changed things revealed vastly outweighs the the things that have been revealed to be the same.