Foundry is not in the business of making a walled garden of content with them as the sole gatekeeper. Just because it doesn't mirror the R20/FGU model doesn't change the fact there is real demand for the products on arguably the most advanced and feature-packed VTT.
Kobold Press, Modiphus, and Cubicle7 are all selling Premium content without any trouble so it's baffling that Paizo just drops a "they don't want to be a licensed partner so welp" and moves on.