I really think theyre overestimating how well KH3 will sell.
Most of the KH fans I know have totally moved on after they started releasing so many different handheld titles across multiple systems and made the plot so convoluted.
There might still be a dedicated fanbase but I dont there are enough people that really care about KH anymore for the game to be as profitable as they need it to be.
The dedicated fanbase is never the majority of sales for anything. I mean I have not played a good number of the KH spin-off games and I will still buy KH 3. It would be like claiming that everyone that goes to see the latest Star Wars film is a hardcore fan.