> I get why you would hide interface elements to use the screen real estate for something else.

Except that screens on phones, tablets, laptops and desktops are larger than ever. Consider the original Macintosh from 1984 – large, visible controls took up a significant portion of its 9" display (smaller than a 10" iPad, monochrome, and low resolution.) Arguably this was partially due to users being unfamiliar with graphical interfaces, but Apple still chose to sacrifice precious and very limited resources (screen real estate, compute, memory, etc.) on a tiny, drastically underpowered (by modern standards) system in the 1980s for interface clarity, visibility, and discoverability. And once displays got larger the real estate costs became negligible.