As a designer, I've been thinking a lot about this "huge amount of whitespace in modern UIs" thing. I personally hate it, I want most things to be always in reach.
Two of my hypotheses are:
(1) some designers are working on huge screens themselves, and don't test enough in usual resolutions
(2) it's easier to achieve good visual composition by doing a lot of whitespace (to the expense of hiding things below fold or in triggerable containers)
