It seems some FreeBSD developers use macOS themselves, instead of FreeBSD. I found this quite peculiar.
My main objection to MacOS & why I don't run it on my desktop is that I can't configure window management exactly how I want it, like I can with KDE or LXDE. Most of what I can't do centers around muscle memory for window management tricks involving mouse buttons and modifier keys. This goes away on a laptop with a trackpad, since the muscle memory is different with a trackpad than with a mouse.
As far as window management, I use contexts for my switcher, rectangle for hotkey-based window management, and stay for automated per-app & per-display window management
There's also alternate window managers for OSX such as Yabai or Amethyst
I guess there are devs who spend quite a lot of time in macOS in order to work on things like https://airyx.org/.