By writing system level macOS software, although I think you mean old style POSIX UNIX stuff.
Here is a thing, already with NeXTSTEP, UNIX support wasn't never something worthwhile looking for, NeXTSTEP was used for its Objective-C tooling and frameworks, like Renderman and Improv.
The UNIX stuff was just a solution for having a quick ramp up for their OS development, and just like Microsoft with Windows 3.1 NT, to have a tick in the box when selling to the government,
Their famous commercial against Sun, hardly touches on UNIX like development.
The only fouls here are those that keep giving their money to corporations instead of supporting Linux OEMs, as Microsoft cleverly discovered.
In fact, had either A/UX not been discontinued or Microsoft seriously supported their POSIX personality, Linux would never taken off, as the same crowd would be happily using these systems.
Here is a thing, already with NeXTSTEP, UNIX support wasn't never something worthwhile looking for, NeXTSTEP was used for its Objective-C tooling and frameworks, like Renderman and Improv.
The UNIX stuff was just a solution for having a quick ramp up for their OS development, and just like Microsoft with Windows 3.1 NT, to have a tick in the box when selling to the government,
Their famous commercial against Sun, hardly touches on UNIX like development.
https://www.youtube.com/watch?v=UGhfB-NICzg
You aren't going to see a CLI on that NeXTSTEP screen.
Just like the SDK is all about Objective-C related stuff, even the device drivers were written in Objective-C.
https://www.nextop.de/NeXTstep_3.3_Developer_Documentation/
The only fouls here are those that keep giving their money to corporations instead of supporting Linux OEMs, as Microsoft cleverly discovered.
In fact, had either A/UX not been discontinued or Microsoft seriously supported their POSIX personality, Linux would never taken off, as the same crowd would be happily using these systems.