Okay, it appears that the whole flat UI fad is due to some retard design manager at Apple, taking over after Job's death:
https://www.fastcodesign.com/1670760/will-apples-tacky-software-design-philosophy-cause-a-revolt“It’s visual masturbation,” says one former senior UI designer at Apple who worked closely with Steve Jobs. “It’s like the designers are flexing their muscles to show you how good of a visual rendering they can do of a physical object. Who cares?”
Inside Apple, tension has brewed for years over the issue. Apple iOS SVP Scott Forstall is said to push for skeuomorphic design, while industrial designer Jony Ive and other Apple higher-ups are said to oppose the direction. “You could tell who did the product based on how much glitz was in the UI,” says one source intimately familiar with Apple’s design process.
But before Forstall, it was Steve Jobs who encouraged the skeuomorphic approach, some say. “iCal’s leather-stitching was literally based on a texture in his Gulfstream jet,” says the former senior UI designer. “There was lots of internal email among UI designers at Apple saying this was just embarrassing, just terrible.”