I'm with BoB on this one, they need the numbered entries to start the hype machine so they can release the crappy cash-in mobile title afterward. I think the only move SE could make that would be rather worrying is if they made XVI or any future numbered entry a mobile title exclusively.

Business wise, the main games need to stick around to promote the other titles associated with it and keep the brand alive within the public consciousness. There is still a bit of a stigma in the market against mobile titles abroad, so I doubt SE would gamble on going full mobile. The worrying thing here is that we may see more crappy spin-off titles like this for all future FF titles.