https://en.wikipedia.org/wiki/Fitts%27s_law
Putting the menu bar at the edge of the screen effectively makes it an infinite sized target so it is much easier to target and select. Menus at the top of a window are easily overshot and missed. Travel distance is easily solved by appropriate acceleration in the pointer driver.
1. Somehow this feels Okay on Mac.
2. You don't actually have to travel the mouse if you use hot keys.
3. The coolest thing the global menu system can give is application-agnostic menu searching.
Nevertheless, if you require that, why not make the place where the menu is displayed configurable? KDE does - it offers 3 options: the global Mac-style menu (which you can put anywhere, even in the middle of the screen if you want), classic Windows-style menus or "hamburger" menu buttons (utterly inconvenient but I'm still glad there is an option for those who like it).
With a menu bar in each window, there's very little chance of this kind of confusion.
Notably, Microsoft managed to bungle this initially in Windows with the task bar: there was a one-pixel gap between the buttons and the bottom of the screen, so you had to aim for the buttons or to readjust the cursor each time. (Though personally I find the downward motion more awkward anyway, both because the wrist action is weird and because the wrist and the wrist support are in the way.)
But yeah, I miss unity too.
This is extra frustrating to me since I absolutely love everything else about the modern Gnome UX, but the refusal to bring in a top menu bar or at least integrate it for powerful apps like gimp, vscode or blender stings and makes it so many times you have 3 top bars wasting vertical space in maximized apps when it could be two or even one.(Activities-button bar, Window title, GIMP menu bar)