Beyond fashion and aesthetics (which are totally valid, and what this article is mostly about), the past ten years of touch UI design have been a process of slowly eliminating the extremely obvious cues that were necessary for a population of user who had no idea how to relate to a touch screen. UI designers have been able to pack more functionality into UIs as they no longer have to beat people over the head with the idea that you can touch the controls.
With the switch to a new UI paradigm (multi-touch) we lost discoverability, predictability through standard behaviour, shortcuts etc... why were UI designers not able to come up with innovations that improve the state of the art? Instead, touch UIs peaked with the first iPhone and since then became worse because more features were added without (I assume) serious usability research.
Instead of attempting to solve the actual problems that need solving, UI designers have retreated into their cozy corner of changing some completely unimportant surface details every couple of months, that's just an illusion of innovation. Smoke and mirrors.