Pretty much was Shoeberto said. Mainly, I think it's the story. Fans want a story with lovable characters, interesting setting, good pacing, and just overall great writing. Of course everyone has opinions and no Final Fantasy can be what every fan wants. But I think most people are in the unhappy camp these days, and even when a majority of fans are saying the same thing, SE doesn't listen.

Oh, and stop all of the spin-offs.