Because the material editor is the worst thing I have ever had to use. It takes far to long to get even a moderately complex material up and running.
I still do projects in Unity when I need to use Vuforia, and their material editor just about throws me into a blind rage every time.
I even got to this thread by googling “Why is unitys material editor so awful” as a way of coping with the shear horribleness of it.
I can’t wait until UE4 has a viable AR platform, then I can finally drop unity all together and work towards reducing my blood pressure