if I had to guess it would be to prevent too many potential US buyers from importing early and maximizing US sales. Being a fighting game I'm sure there's quite a few super hardcore persona fans who would have no problem importing assuming it would be easy to understand.
From: LordEmbok | #006 how does a fighting game have 30-40 hours of single player content? is this subspace emissary times five Maybe that includes clearing arcade on max difficulty with every character?