Eh? No, there are already female Ronso designs to base the female Hrothgar on, if indeed what they wanted to do was have the Hrothgar be carbon copies of the Ronso like the Viera are of their XII counterparts.
If there was a singular reason they didn't go with female Hrothgar, it would be the overwhelming fan demand for Viera and the disappointment that would result if they weren't introduced. As this is being billed as the last time ever new PC races are introduced... as a guarantee, at any rate... they felt forced by that selfsame fan demand to implement Viera. From what I understand, left to their own devices the devs would have just added in the full Hrothgar.