More than anything hamburger menu type design feels to me like an “avoid effort and skill as much as possible” sort of thing more than it does an “optimize ad revenue” sort of thing, as does flat design. It’s about lowering the bar for what’s acceptable to ship as far as you can possibly get away with. Plaster some scrolling flat rounded rectangles and a hamburger menu on the screen and boom you’ve got an app.

Don't make me think? Don't let me think!

I had to look up "CUA".

Common User Access (CUA) is a standard for user interfaces developed by IBM to provide consistency across operating systems and computer programs.

The Palm menubar wasn't permanently visible, the Palm had as close as you can get to a hamburger menu to reveal it https://kalleboo.com/linked/palm-burger.jpg