For those who suggest that hair and a helm can somehow coexist on a model simultaneously - you're wrong, they can't. It's either one or another.
(Same as in DAO or DA2, by the way.)
In order to combine both an artist'd have to make a unique hair+hat model.
And now, for those who have plenty of time to spare - feel free to do the math about the exact number of possible helmet+hair combinations in DAI.
Their only mistake was introducing those fancy hats beforehand, which looked good for a demo shot, but which could not technically be implemented with a CC character. This, and keeping them in game.
Surprisingly, some of companions have their hair on - I think I've seen Blackwall like that, must be a leftover from the initial idea to make a 'haired' versions. But, again, companions only can have one preset haircut, unlike PC.