Windows was a virus laden mess and was not useful for running Linux apps.
And besides the flaws of the other OS’es, OS X had some of the nicest window management features (Expose from the Snow Leopard is still my favorite window switcher), was a UNIX and had a thriving indie development scene (which was basically killed by iOS…).
Since then OSX has completely languished as a developer platform. It’s not clear what you can do today as a developer to make your life easier that you could not a decade ago on OSX. And in fact, the destruction of the indie dev scene, combined with the many heavy handed security restrictions of dubious benefit have made it a far worse dev environment than a decade and a half ago.
Further, Linux DEs have greatly improved and Windows now supports Linux development.
The Mac ecosystem has seen a complete turnaround where you now buy a Mac for the hardware, not the software.