Yes, the ability to develop mac, iPad and iPhone apps.
That and people may just generally prefer using the actual OS over the other two.
I can't stand using Windows for anything other than playing games, for example. I've also never been won over by Linux for anything other than working on the command line only.
Also the way macOS handles 'spaces' (i.e. multiple desktops) especially when connected to extra monitors is unmatched on any OS with a decent gui
On top of that, every mobile developer I know uses a mac because even if you're an exclusive android developer, at some point you will likely be asked to look into writing code for ios, or be asked to work on a cross platform solution which still requires access to xcode.
That and people may just generally prefer using the actual OS over the other two.
I can't stand using Windows for anything other than playing games, for example. I've also never been won over by Linux for anything other than working on the command line only.
Also the way macOS handles 'spaces' (i.e. multiple desktops) especially when connected to extra monitors is unmatched on any OS with a decent gui