One aspect that I think is crucial is to the stagnation of Mac software is the lack of good documentation and books. Most of what you find about developing apps

One aspect that I think is crucial is to the stagnation of Mac software is the lack of good documentation and books. Most of what you find about developing apps with Swift is focused on iOS. If you ask anyone about good resources to learn, they point you to scattered WWDC videos and personal sites of cool developers offering video courses and tutorials. This is very different than what I remember from when Mac OS X was introduced. I remember getting big fat books from Big Nerd Ranch and having wonderful documentation to me as I learned the basics of Objective-C and Cocoa. I've been trying to get back to desktop app development after more than 10 years doing web stuff, and if feels like a totally different place. Heck, there are stub pages at Apple that only list the function signatures and nothing more?! WTF! There are no recent books about developing for macOS.