I switched from Windows to Apple around 2010, after using Windows 7 for a year, and away from Apple a year or two ago, after Mountain Lion.
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.