I like that Unity puts the global menu on the side. This makes more sense with all the wide-screens that we have nowadays. A huge oversight in MacOS, if you ask me.
On macOS only the dock can be moved to the side. The application menu (left) and the statusbar menu (right) will always be on top of the screen.
Which makes sense to me.
I agree that the side is better and would be a better default. For the record, the location of the MacOS Dock is configurable — I have mine on the right.