Something similar happens in web pages where you're supposed to click a link but the styling doesn't it allow to be a conventional link, so you don't know where to click. Interface designers have a responsibility to not break usability if they diverge from well known widget styles.
Or ... making some stuff larger but not others.
In OSX, I can use a slider to make stuff 'bigger' in Finder, but... it only increases the icon size, not the text size, which makes using the UI from a distance impossible, even though they've got "make stuff bigger" built in.
OS X is freaking gaudy and I hate it. Apple as a whole just has no freaking taste these days. I just want a clean, intuitive interface that lets me run my programs and stays out of my way.
The Amiga Workbench (well, 2.0 onwards. The bright orange-on-blue color scheme of 1.x was rather distracting) was really quite nice.
[sorry, clicked on wrong reply button]
Even in Windows 95, each program in the programs list didn't look like a 3D button. That inconsistency can be confusing too.
In a way, a menu is a large button with horizontally separated segments (each row of text is its own clickable area, and there's nothing else in the menu).
IMO, pseudo-3D appearances like Windows 95, NeXTStep, Mac OS 8, and early KDE/GNOME were the pinnacle of aesthetic GUI design (and Windows 95 in particular is the pinnacle of UX as a whole), and everything since then has been a step backward.
I think about the only GUI aesthetic I can stand that's come out of the 21st century has been the use of transparent glass on some elements, and that fad has already died off, sadly. I have my KDE configured to look like a Windows 95-ish design (i.e. pseudo-3D and gray) for most things, but render a small handful of other things with glass, and it works pretty well for me.
While I do hope that this is "just a phase", I don't think it will pass too quickly. The one thing that flat design excels at is quickly and cheaply creating "compliant" UIs and associated elements.
A former colleague of mine sketched the situation bitterly over a few beers; ten years ago or so, he'd spend days, sometimes even a week on an OS X application's icon. It was exhausting and it was hard to convince clients to pay him a week's worth of hourly fee for a damn icon. Nowadays (well, nowadays was about two years ago, I think), he could have two or three mockups ready in an evening and the hip entrepreneurs he worked for on the side would fall off their chairs gasping at how "clean" and "intrinsically meaningful" those blobs of colour were.
We joked around that a lot of the activity could be automated by just writing clever software that takes a 3D picture or a good enough photo of something and makes a "flat" version of it, requiring only a little intervention on a vectorized version to get something final-ish. Voila, icon "design" as a service.
There was a classical canonical sweet spot in this era design mindset. Kinda like going into a country side cabin. No fancy stuffy, yet most things are just like they need to.
ps: It's hard to remove nostalgia / habit bias; but I consider myself far from prejudiced, having gone into almost all UX fads since I had a keyboard and a mouse. I accept qualities in all systems be it Apple, Linux, Amiga, SGI, HP handeld calcs and all kinds of different ergonomics (CAD, Compositing, Video, Audio, code, shell, IDEs, Smalltalk) ... And even after seeing all of this, Old Windows (until 2K) had a nice sweet spot feel.
I don't use Windows these days, but Linux GUI programs are not as well-designed as the old Windows programs, so I find myself reaching for the mouse every now and then.
I find it slightly useful -- I can usually visually guestimate a tool's graphics toolkit and predict its behavior, but novice users will almost certainly get confused.
Like you I find environments I cannot keyboard control are hugely unproductive.
Plus ca change...