Basically all the reasons that have already been mentioned:

1. Possibly with the exception of Genesis3, it does not appear to me that any of the new figures are particularly any better. That even goes for Weight Mapped V4 that doesn't seem any better to me than just normal V4.

2. Price, time, and effort to adapt to a new figure. Unless they are going to offer me something really exciting, then why should I spend all that money and time to adapt my current content to the new figure?

If you want me to adopt your new figure, then you have to show me something it does that V4 can't do. And that something needs to be something that makes me stop and go, "Wow! I need that in my runtime right now!!" Nobody has done that, except for Genesis3. Although even Genesis3 hasn't made me stop and go, "Wow!" It just seems obvious to me that Daz is constantly making improvements to Genesis and that has me considering the move to Daz4.

I have workflow that does what I need with a figure that I understand and does what I need with tools that I mostly understand and that do what I need. You better blow me out of the water with what you have to offer if you want me to change all that. And one of the most critical areas for that is screw ups. I basically have the tools, and sort of understand them, to fix anything that goes wrong with V4. If a pose, morph, or clothing goes totally sideways, then I can probably fix it with V4. I cannot say that about other figures.

But I will be 100% honest here too - I have not tried any of the other figures, including Rex or Roxie (though I keep meaning to).