I think they didn't fix it because they didn't think it's a problem. I understand it might be hard to get used to if you're used to using applications fullscreen. But when you use a 27" iMac you kinda get why it works that way. I just have a lot of big windows and actually never want to maximize any of them. Partly overlapping windows also makes it easy to switch between them. So it actually suits the way I work quite well. As I see it: Apple has a vision on how you are supposed to work with a computer. You can only change it slightly. Maybe you like it, maybe you don't. I generally like to adapt the ideas a UI or OS is using. As long as it feels coherent and well thought out.