To all on the list and this thread: Why did the “flat look” come into vogue? In the Linux world, it’s also crept in with the GTK3 widgets. Was the driving force tablets and mobile devices?
Sometimes it’s change for change’s sake. Any UI look and feel that’s been around for 10 years looks old (because it is), so you change it and now it’s new. And yeah the new look might not be as aesthetically pleasing, but it doesn’t look old and that’s good enough, and it too will be gone in a few years.
From Mac System 1/Windows 1 until a couple of years ago, icons just sort of evolved without any particular plan. Meanwhile, people became accustomed enough to graphical interfaces that they didn’t need the visual cues of mimicking real-world objects. All the drop shadows and skeuomorhism just became clutter.
There’s certainly some trendiness involved, but there are also practical benefits to having a common visual language. Kind of like how floppy disks and tractor-feed printers survive in icon form, easily recognized by kids who’ve never seen the real thing.