Because they are intelligent businessmen and they know that by creating and marketing low budget and relatively inexpensive movies, spinoffs, and sequels, they can make more of a killing because the name they put on it. They realize and understand that Final Fantasy is a cash crop and they are using it in the best way possible: to make as big a profit as they can by selling entertainment items that do not cost a lot to make.

I just drank a "berry injected" Vault Red Blitz. Have you ever tried one? How delicious do you think it is? (On a scale of 1-10, 1 being delicious and 10 being super delicious)