Any prop in particular?
I don’t generally use DS so I’m not sure if it saves props in pp2 format natively. There used to be a Poser format exporter for earlier versions of DS but I don’t know if it was ever incorporated into the DS4 Pro version or updated for it.
Some vendors may not have Poser or even have much familiarity with Poser formats. Some may have been created before the DSON and duf and have never been updated from the dsf files.
In the end, I suppose you would have to ask the vendor. I do know some PC props that were originally released with duf files only to have the pp2 files when it was brought up.
If it’s a DAZ Original, you might want to contact DAZ. If it’s a PA item, you would need to contact the vendor.