Exclusivity isn't the issue. If Sucker Punch can sell over 10M units of a new IP, then Square Enix doesn't really have any excuse here with such a storied and beloved series like Final Fantasy.
Perhaps they should've made a better game, both on the technical front and when it comes to actual level and quest design, without so much bloat and nonsense that adds nothing to the experience. Maybe then it would've moved God of War-level numbers, as Final Fantasy should do as an iconic PlayStation series.
Or perhaps it all comes down to how fucking bad they screwed Nomura over a decade ago, when they removed him from his dream project, Final Fantasy XV, only to let that useless hack Tabata run it to the ground while not staying true to any of the concepts that captured people's interest back in the Versus days, totally blowing what could've otherwise resulted in a grandiose trilogy of games and leaving an awful taste in modern players' mouths that lasts still to this day.
You reap what you sow, Square.