It depends on what we're talking about. I would expect UI design elements to merge where the capabilities of devices are converging. That's not happening from the desktop since Apple is against desktop touch input; if anything the mobile side should be moving closer to desktop, but that's not happening either. I would also expect UI designs to be merging where innovation is concerned, say if they invested in better desktop/window manager UI, but in actuality all that is happening is the backporting of iOS ideas that are all centered on the fullscreen mode.
> I wish they would spend time looking at some of their interface changes and really work extra hard to help non-techies "get" them
In my experience that's not really a pain point. I have seen several of my clients adopt an OS X-only landscape in their offices (mostly non-technical people). I feel Apple is actually making heavy inroads in office and home use, but for many reasons is losing the support of technically-minded people who - at the risk of sounding self-absorbed - are early warning indicators that the base of the platform is withering significantly.
And—look—the way the desktop works is not going to be changing drastically any time soon. Their is not much to innovate on, so the obvious next step is to perfect every single interaction and to fine tune every single component of macOS (or Windows or any other OS) to make it faultless. That will keep me and many others around. (And keep trying to innovate and revolutionize in the backroom)
I'm inclined to agree, but we're starting to hit the zone where I feel I'm using a tool of questionable qualities because of lock-in and the absence of sane competitors. The Unreal Engine IDE runs at 10 fps on my current-gen iMac, an expensive machine based on 2010's hardware and no upgradeable parts that takes minutes to boot up into an increasingly DRM-plagued OS where all the innovation goes into iOS-like features I don't use.
> so the obvious next step is to perfect every single interaction and to fine tune every single component of macOS [...] to make it faultless
I disagree vehemently that this is what's going on. If that was the "problem", my (software) complaints would not exist.
I imagine like Iron Man where he can divert resources to his weapons from his thrusters and stuff. They do keep adding things that need to run when I wish I could selectively turn some things off.