They could literally not even add the horn options to any other race, even though it should theoretically be as easy as adding in helmets as cuatomization options; they already have placement points for doodads like that. But Chromie and Ebonhorn don't have horns. Theyre choosing to look like mortals.
I just dont see why they should be so limited to blood elf male and human female. Any of the time they spent on the visage form (and they spent A LOT) could have been used to give scale options to the other races, or adding new hairstyles to existing races.