> the vast majority of users are developing for macOS and iOS.
The vast majority of Swift users are developing for iOS.
The article is about macOS and private API. Thus it's only relevant to a small subset of developers who write native Mac software distributed outside the App Store.
Note that https://www.reddit.com/r/iOSProgramming/ is itself also extremely active with posts within the last hour, so it's strange to cite r/Swift as evidence of Mac activity.
Granted Swift is technically a cross platform language but it feels safe to assume that the vast majority of users are developing for macOS and iOS.