That's the challenge with these sorts of things.
I know I could convert the Pirate Borg classes to Shadowdark super-quickly, for instance, but if I put what I've done out there in the world, doesn't that harm Limithron?
I have similar concerns over converting monsters, treasure, spells, etc., for other systems. I'm more comfortable doing conversions than most people, I think, so putting that stuff out there would likely be helpful to a lot of people, but taking away even part of the financial incentive for people to make their original content that I then convert isn't something I ever want to do.
(If any companies want to have me convert their content to Shadowdark and then have them publish that themselves, I'd be thrilled to do so. I actually reached out to one company that had expressed fondness for Shadowdark about the idea but never heard back.)