Surely now, given the way in which DS4 has apparently branched away from Poser in terms of functionality and compatibility, this is a bit like asking why all vendors don't make products that work in both Vue and Poser?

The answer is, some do, some don't... but they're distinct applications, with, now, reasonably diverse compatability issues to contend with.

A lot of vendors will only have the resource (or indeed inclination) to focus on making items for any one given program?