With Windows and Mac both, it wasn't any one thing in particular, just a "death by a thousand cuts", so to speak, of a general feeling of the platform changing shape without me having any say in it, without any bi-directional feedback, just changing at someone else's whim, and having little power over it.
Not only was it changing, but it was continuously disempowering me, with more and more things becoming controlled by the OS system, also without me having any say in it.
In the beginning, with Windows there was the seemingly additional friction of the whole drive letters and backslashes thing, and my doing most of my development in GNU-land... But then I realized that Mac GNU is almost as far away from what I develop on anyway, and I found it more comfortable to use a GNU/Linux VM to write code on anyway. I only used Mac for stuff like media playback and low-risk web browsing.
After that, it was only a matter of time.
Stallman was right, and I'm so grateful to have this wonderful platform which works reasonably the way I want it to, doesn't upgrade without my consent, and is infinitely configurable and meldable to my liking. Sure, there's a whole slew of crap being grafted onto it like systemd, Wayland, Chromium, etc... But it's all optional, and I don't have to use it. Thank you, GNU, thank you rms, thank you all the devs! I'm forever grateful to you for all your hard work.
But... you don't have to use any of this
(in fact, I can't even use Wayland at all, even if I wanted to [because of Nvidia])
There’s no such thing as "Mac GNU", since the userland and outermost kernel interface is of BSD lignage.
Which does a double whammy on the "GNU/Linux" pedantry, since the Linux-based system described above has only a very limited part of it that are actual GNU projects, or even GPL licensed.
That is, unless I’m mistaken and parent uses a system without Xorg, and only lives with bash, glibc, make, GCC, coreutils, and emacs. GNU/Linux is quite an ascetic system these days.
first thing I install on my macs are the gnu coreutils. bsd are so useless in comparison
The state of the Windows UI now is a disgrace. Its design defects and lack of organization confound users of every expertise level, and its defects make every task a day-ruining ordeal.
Microsoft even took away one UI facility that always made it superior to the Mac: user-definable color schemes. WTF? I was using my own "dark mode", a charcoal color scheme, since the early '90s. Now I challenge you to find the color-scheme editor in Windows. Just as everyone finally realized that inverse color schemes are stupid, Microsoft started forcing one on you.
And it doesn't look like Microsoft has any inclination to overhaul its failed mess. But really, what motivation do they have? Who uses Windows now who doesn't have to do so for work, using some specific software?
Even Visual Studio, which I held out as the gold standard for IDEs, suffers from the same dumb defects it did 25 years ago. They were tolerable then, but now everyone else has caught up and surpassed it. Even Xcode.