I don't think the problem is so much specifically the hair, but the lack of quality and attention in comparison to the other three races. It feels very rushed and lesser, and that's (at least mine) the main objection.
I would say it's a matter of both quality and quantity.
The hairs, when shown in the CC demo, appeared to have less detail and poorer texturing when compared to those of other races. That is big problem.
But it's more than that; there were only 3 actual hair meshes (plus a bald option which requires no hair mesh) for the entire race, repeated multiple times with a few different horns, so hair in general is a pretty big problem. It means that no matter what option you select, you're only ever seeing those same three. Rather than 20 unique options, there are a bunch of pseudoreplicants that overlap significantly, dramatically reducing the likelihood of having style/horn pairings that appeal to different individuals. So even though the horns are nice and fairly diverse, they are not very well complimented.
Considering how prominent hair mods are and how many topics appear regarding hair, I don't understand the rationale.