Spirits Within failed because they slapped final fantasy title on something that was a piece of crap to begin with, and did nothing but infuriate the fans for spending $8 each to go see a big fat lie.

It would be mildly successful if they made a movie, with ACTUAL ELEMENTS OF FINAL FANTASY in it. ya know... magic, chocobos, moogles, airships, Cid, black and red mages with their iconic hats. Include at least 2 or 3 of the above icons, make it a good story that fits into 2-2.5 hours of a movie, and profit

They wont do it though, they are too chicken after the monumental failure of Spirits Within, because they lied to their fans about making a FF movie that clearly wasnt FF.