Because the gender is absolutely irrelevant to that title in particular. Its in direct response of desposing Ragnaros and claiming his title. The title is genderless due to the position its refering to.
One would be deemed firelord regardless of gender.
Actually, while this might be true, the fact that Therazane, another elemental lord has the title of “Earthmother” or “Stonemother” suggests that the elemental lords chose their titles.
Another point is that we do not even know if “gender” exists for elementals, since the concept of reproduction is pretty different from ours. If this were to be true, what would apear as their “gender” would just be a simple quirk of their personalities.
Overall I do not care if they wanna change/add a “firelady” tittle or whatever, just give it as an additional title so that people that want “firelord” on female characters are also happy.
On topic.
If it were Lord Fire ( 2 words with Lord as the honorific) it would be gender specific, but as one word Firelord I don’t see it as a gender… just my opinion.
Would be Blizzard being Blizzard again. Baine confirmed Azeroths title is Earthmother and always refered to her with that in reality. That would leave therazane with Stonemother unless she wants to fight (and die) Azeroth for the title.