I didn't really think FDL was that big, but I guess I never noticed until now. I'd have to agree with everyone who said it might be because he's too powerful that you can't use him everywhere. I had always imagined that FDL was only necessary to combat something equally as strong, so if nothing is in comparison, then it's like the FD mask's got its own attitude and it's uninterested because of how feeble everything is compared to it.
That's why I wanted to bring up the FDL aspect of a Zelda story because it's almost unfair to only use FDL in boss battles. Yeah, it makes things sweet and you get to straight up own, but at least devote an entire level, or place of some sort where you can freely roam as FDL. I have intentions of reaching this point where FDL can roam in The Legend of Zelda: The Cardinal Kingdom; there is a specific kingdom so corrupted by evil, etc. that FDL is on full alert at all times, allowing the gamer to fully utilize his abilities. Other than that, I wouldn't want to give FDL too much spotlight just because to me it's like a last resort transformation.