1: It's easier and faster to use IFF you spend the time to learn it.

2: Information density. It actually uses the whole screen, and isn't designed around applying (and taking to the extreme, which is the style at this time) the concept of negative space one learns in design school.

If I open youtube's homepage in a maximized window on a 1080p screen I see: two video thumbnails in row 1, with the right third of the row just blank, and half of row 2, containing 5 short video thumbnails (the utterly useless ones), the lower third of which is offscreen. Insane