Exactly. There may have been a reason for the single menu bar back in 1984 when the Mac had a 9-inch screen. But it doesn't work very well on my 43-inch screen where the menu bar may be a few feet away from a small window in the lower right hand corner.
That isn’t obvious. With a mouse/trackpad with a good acceleration curve, chances are you can move faster to that menu at the top than to a menu a few cm away because you don’t have to decelerate when approaching the menu bar at the top of the screen.
Follow Apple's logic, reductio ad absurdum, and you'd have to put every single GUI element in the corners of the screen, because how else could you manage to quickly select them with a mouse? That OK button in the dialogue? Top right corner of the screen. Cancel? Top left. Quick, easy, and nobody could ever press the wrong button. It'll make it faster!
Resizing windows already requires moving the mouse with single-pixel precision. In comparison, hitting the menu bar is very easy.
Also, these menus are very consistent in appearance, functionality, shortcuts, etc; moreso than my experience with Windows applications.
I've seen this in webpages too. You load a page and think there's an error but the "login" button is surrounded by so much white space that it doesn't show up in the browser until you scroll down.