While I agree that the OS X APIs were superior at the time, it is important to remember that Windows was and still is an enterprise OS, first and foremost, and

While I agree that the OS X APIs were superior at the time, it is important to remember that Windows was and still is an enterprise OS, first and foremost, and this is a big mess. So this slowed progress a lot. Modern Windows UI frameworks are good too, but they are used very seldom, or if used, often used incorrectly. Since high DPI displays have been rare and expensive, I think also developers have very little awareness of the problems, and much less will to work on it. Linux is in the same boat.