it's supply and demand.
- maybe some highly skilled daz product creators are no longer active?
- maybe not many gen9 products are sold compared to gen8 currently? (many buyers take some time to move across to the new products if they have a good library of previous gen contents)
You can create the feeling of demand by asking creators who made Gen8 tools that you want to buy on Gen9 to do the work (contact them via daz forums and encourage them). If you are just pirating the creator's work then maybe they don't want to spend the time for a small reward.