Originally Posted by
LaylaTsarra
"Yoshida added that in Final Fantasy XII, which is where Viera is from, the male Viera do not show themselves in public, so Final Fantasy XIV Online is staying loyal to the lore with only offering a female option. Yoshida explained that the male-only Hrothgar is Square Enix's effort to offer a new male-only race in response to Viera being female-only."
The above certainly appears to be the reasons for the route they took with the race choices. Can that change and lore be revised and additional genders added, certainly if they choose to do so.