>>96806779
Up until relatively recently (2019) they were only available in metal and had bad rules if they had rules at all.
They were almost completely forgotten about the very end of 8th edition. They were not included in promotional material and were in one single game. For most people they are still a new faction that they are able to collect, 90% of people will not have seen their metal models.
Theres also how detailed they are and I think that does have an effect of them. Plus a lot of people dont know how to paint female faces
I also think part of it is many people just not wanting to play an all female faction for whatever reason