Well... It would be an awesome thing to see them implement, but... I can also somewhat see why they're not. Admittedly, my knowledge of Japanese culture (current and historical) is coloured by various media (movies and books that are fiction and thus aren't necessarily correct, and manga which tend to exaggerate certain things, and non-fiction books that more often than not get confused between various Asian countries and cultures), so if anyone knows more details or knows that I'm wrong, feel free to correct.
Ages ago, being left-handed was a huge stigma over here (i.e. in the West) and could get you executed for witchcraft or stuff like that (there's a reason why 'sinister' means evil, after all). Today... people don't generally care if you're right-handed or left-handed.

In Japan, it wasn't as much a stigma in itself, as long as you did things correctly -- i.e. eat with your right hand, write with your right hand (cos otherwise the characters don't get drawn correctly, I assume), and use the same fighting stances that right-handed people use. As for how it is today... I haven't really heard much regarding left-handed people in Japan, so I'd assume it's close to the same? And if that's so, I can understand if the developers don't see it as an issue, because 'it wouldn't matter if the Warrior of Light was right- or left-handed, because they'd be doing things the same either way'.

But even if that's the case, I would hope it gets considered, since they're making an international game.