Thanks for that perspective! I think that dynamic is present in quite a lot of other communities too, especially the ones who have not traditionally embraced open source. You also see it a lot around creative / artsy work where it almost seems to be a faux pas to share anything but the final product. People do recreate things or just are inspired by other work. Coming from open source software it always seemed like wasted potential to me, but that's probably just my bias.

> In a sense, these mods are no longer open source, but rather source available

I understand what sense you mean, but the terms "open source" and "source available" have very clear definitions, and it has nothing to do with accepting contributions or not, only with the license the code is published under. So in a sense only about downstream effects; upstream effects are still a courtesy also with open source.