As we added feature after feature to Mjolnir, and it grew to a monolithic collection of barely-related modules (APIs), I realized that it didn't make a lot of sense for users to keep upgrading to "newer" versions of Mjolnir, when in reality it was just the modules bundled with Mjolnir that were new or changed, and Mjolnir itself wasn't changed at all.
So I made the decision to decentralize the APIs. Instead of being bundled into Mjolnir itself, users would be able to download Mjolnir and then download or upgrade modules independently of Mjolnir.
This was pretty unpopular, because it meant Mjolnir was no longer "batteries included", so Hammerspoon was forked by the portion of the community that preferred that batteries included approach. Honestly, I don't even know how much of the community (if any) continued to use Mjolnir.