Allowing a choice of gender would involve doubling much of the dialog, artwork, etc. Choice is good, but I wouldn't want to sacrifice on plot or quests, etc, to get that in.
In Divinity 2 you could choose (and change) your gender, but other than voice it did not have much of an impact; there were few places in the game that even acknowledged your gender, and only one quest (in FoV) that depended on it.
Personally I've played games/RPGs with pre-set male and female main characters, and when given a choice I have created male and female characters. Generally the difference is pretty superficial, IMO.
Besides, having a skeleton princess with a couple apples stuck in a dress is innocuous and slightly amusing. A skeleton prince similarly stuffing clothing might run afoul of the rating boards.
