I think a lot of vendors left due to the fact poser is pretty archaic when it comes to content creation. I think they saw there was more money to be earned with Daz studio and they dabbled into it. Then found out it is just a few clicks to pack your content and ready to upload.

Or course Daz has been using poser for years and knew exactly what posers shortcomings where and arem and when they built their software they where able to avoid those mistakes and shortcomings to some extend. Basically poser still runs on the same old software engine and they just add lines to update it. Which also means extra new bugs ( like some features of cycles are not being able to being implemented) Daz studio is newer so they have less of a problem with those things eventually they will run into things like this too. Or they rebuild the sofware from the ground up.