This is like a Pokemon spin-off. It has the things that make it part of the franchise, which would be the Pokemon, but each spin-off has its own purpose. Like in Pokemon Mystery Dungeon games you don't get to catch and train Pokemon, or battle gym leaders, etc. which is what makes the main games of the series, but it still has the Pokemon, which makes it part of the franchise. And the Mystery Dungeon games have their own goal, which is to be a Pokemon and save the world from destruction. Most of the core features that make the main Pokemon games special are what's missing from the spin-off games to be replaced with other things unique to the spin-off, just like with HHD and the main AC games. Here, having a customizable town with villagers to befriend is replaced with designing homes for villagers and other community buildings, making it its own unique game. The whole point of a spin-off is to be alike the main games enough to be part of the franchise, but to have its own special features as to not be one of the main games itself.
I'm not sure if that helped you understand why it's not part of the game and why that complaint isn't really valid, considering it's a spin-off game, but I tried.