SE did't ask us but if given a choice what you rather have?

1) F Viera & M Ronso
2) F/M Viera
3) F/M Ronso
4) F/M Viera & F/M Ronso

SE chose 1. The player base might have chosen 1, 2 or 3, we we never asked.

The devs and the players both know choice 4 is by far the best, but it just might not have been feasible at the moment. I frankly won't be surprised if come next FF Yoshi announces they are adding the other genders.