I think that main problem that they would have with changing head models now is helmet models for lizard. Because if they would made lizards with heads of different sizes they would have to change models of helmets too, and I do guess that is not small work.
I also agree that there is no need for lizards with hair just does not fit well with race in general. (imagine lizards with bears)
Though I gotta say that if there is option to put beards on undeads. I am putting it on mine undead
