Its as reasonable as your assumption over the decision making of a creator of his own series.
Stick to playing games.
I made no assumption over the decision making of the creator. And yours is not a reasonable comparison at all. Xbox One is a strange naming convention that pays no attention to numerical order. KH3 has a three at the end because it continues the main story arc last visited in KH2. Sure, all the spinoffs have important details for KH3, but there's nothing unreasonable about me wanting them to get back to the story and stop complicating it with all these side stories. And there's nothing unreasonable about calling a deck building card based battle system with "worlds" that are just skins over a castle's walls like Chain of Memories a spinoff to a game about traveling between Disney Worlds through interdimensional travel and fighting with a traditional ARPG fighting system.
And I'm not here to play games, I'm here to discuss them. If you want to play games, VGChartz is not where you should be. It's a forum. Not a game console.