Modkits/SDKs
If you want a thriving mods community, you should provide tools to make things either possible at all, or just easier. While community created tools can cover many bases that developers won’t, it always makes sense for official tools to be created.
While I create modkits for multiple games, I can see the scenario where I get burnt out and stop maintaining my tools. Even though I try to document as much as possible, if no one picks up the slack, entire modding pipelines can grind to a halt or be reset to square one. If the developers created official modkits, there is an obligation to keep things maintained and documented clearly so that the next developer can continue the work. Modkits may only need to be updated per major update, so if the game is no longer updated, then the final modkit will be in-line with the final game version.