Can you help me understand why this mod's updates aren't being submitted to Paradox Plaza & why this mod lives solely on Steam?

Walled gardens such as Steam are infuriatingly discriminative. What is inhibiting this mod from getting its updates published through Paradox especially given Paradox' recent push for cross-platform support? Many Stellaris players have purchased this game through other platforms and publishing exclusively through Steam denies them access to your gorgeous mod.