This isn't just a difference in UI, but also in the way the OS handles processes. Under macOS, the vast majority of programs host all windows under the same pro

This isn't just a difference in UI, but also in the way the OS handles processes. Under macOS, the vast majority of programs host all windows under the same process. In other words, windows do not represent instances of apps, even under the hood. You can spawn additional instances of an app with the terminal, which will give each instance its own dock icon, menubar, and set of windows. So shifting window closing behavior to function like that of Linux or Windows would actually require a much more fundamental change than it might seem.