Well, that's because every other that did atleast 1 set knows how much of a pain in the ass it actually is, and in the end the time you spent on it is not as rewarding as making multiple heads in that time.
I just made 2 Sets, a jointed one and a non-jointed one. I think i spent about 2weeks on the non-jointed one and made 45k of it and the jointed one.... i dont know anymore, something between 4-7weeks which i sold for 243k .
Now, don't get me wrong, 243,000tc sounds pretty nice and all but comparing it to the time spent on it, the effort and hand-mapping pain i could have just drawn alot of heads.
It was a nice experience to make a good jointed set but i couldn't raise up that much time again for one and declined or cancelled alot of the request i got after selling it.