And most people are not figure designers. They're texture artists and dial spinners. 

When you're designing a figure its an entirely different field. 

You have to consider the market you're designing it for, who you want to use it and what you want it to be capable of, all while looking at all the other figures that are currently available.  Then find ways to make content creation for that figure easy on the vendors that you hope will support that figure.

Poser provides most of those tools, and the means to incorporate scripts that will add features in for the tools that it doesn't yet have. It just doesn't provide a figure that utilizes those tools to the best of their advantage, and so far no one else has actually put the effort in to designing a figure that does either. 

Actually no, some of us have.