Windows programming guides provided by Microsoft were simply amazing for the time; the documentation available was excellent.
Part of the reason they did so well, companies could easily implement software using the new APIs.
Of course, they also had secret and undocumented APIs that people found and wanted to use ...
This and great backward compatibility. I still can make app targeting Win2000 and it will run on Win2000 onwards (Win10 and Win11 included.) Unfortunately, its starts to fall apart...
I guess they finally think they captured enough "value" with Windows so there is no need to keep every subsystem maintained. It must be very expensive to keep a 20+ year developer to sit in a basement room writing code for some feature that does not generate much revenue. Sad truth. TBH I'd love to learn those subsystems and do it for free.