With 320x480 iPhone screens, we had to be economical for navigation, tools, and the content view. (BTW, the content view is UI. The entire app is UI.)
Screens got wider and taller, which gave us more space for the content view, without having to sacrifice navigation and tools.
But look what happened. In many cases, it actually got much worse, with vertical space eaten up by things that were never even visible before.
So why are we now sacrificing navigation and tools?