a lot of the kernel extensions are closed source proprietary. The core is still open but a lot of what makes modern Mac, Mac, are those kexts.
By referencing the 90s it is a reminder that Mac started on an entirely closed source kernel. It's a regression towards the Mac mean more than a regression away from it.
how has that changed over the past 20 years? the proprietary parts of Mac OS X and now macOS have been proprietary from the beginning