You're absolutely right, Jim.
The last big advances were in the 1990s, and since then, things have just stagnated. There are several reasons why -- like all of real life, it's complex.
Firstly, many people believe that computing (and _personal_ computing) began with the 8-bits of the late 1970s: the Commodore PETs, Apple ][s and things. That before them, there were only big boring mainframes and minicomputers, room-sized humming boxes managing bank accounts.
Of course, it didn't. In the late '60s and early '70s, there was an explosion of design creativity, with personal workstations -- Lisp Machines, the Xerox PARC machines: the Alto, Star, Dandelion and so on. There were new cutting-edge designs, with object-oriented languages, graphical user interfaces, networking, email and the internet. All before the 8-bit microprocessors were invented.
Then what happened is a sort of mass extinction event, like the end of the dinosaurs. All the weird clever proprietary operating systems were overtaken by the rise of Unix, and all the complex, very expensive personal workstations were replaced with microcomputers.
But the early micros were rubbish -- so low-powered and limited that all the fancy stuff like multitasking was thrown away. They couldn't handle Unix or anything like it. So decades of progress was lost, discarded. We got rubbish like MS-DOS instead: one program, one task, 640kB of memory, and only with v2 did we get subdirectories and with v3 proper hard disk support.
A decade later, by the mid-to-late 1980s, the micros had grown up enough to support GUIs and sound, but instead of being implemented on elegant grown-up multitasking OSes, we got them re-implemented, badly, on primitive OSes that would fit into 512kB of RAM on a floppy-only computer -- so we got ST GEM, Acorn RISC OS, Windows 2. No networking, no hard disks -- they were too expensive at first.
Then a decade after that, we got some third-generation 32-bit micros and 3rd-gen microcomputer OSes, which brought back networking and multitasking: things like OS/2 2 and Windows NT. But now, the users had got used to fancy graphics and sound and whizzy games, which the first 32-bit 3rd-gen OSes didn't do well, so most people stuck with hybrid 16/32-bit OSes like Windows 9x and MacOS 8 and 9 -- they didn't multitask very well, but they could play games and so on.
Finally, THREE WHOLE DECADES after the invention of the GUI and multitasking workstations and everything connected via TCP/IP networking, we finally got 4th-gen microcomputer OSes: things like Windows XP and Mac OS X. Both the solid multitasking basis with networking and security, AND the fancy 3D graphics, video playback etc.
It's all been re-invented and re-implemented, badly, in a chaotic mixture of unsuitable and unsafe programming languages, but now, everyone's forgotten the original way these things were done -- so now, we have huge, sprawling, messy OSes and everyone thinks it's normal. They are all like that, so that must be the only way it can be done, right? If there was another way, someone would have done it.
But of course, they did do it, but only really old people remember it or saw it, so it's myth and legend. Nobody really believes in it.
Nearly 20y ago, I ran BeOS for a while: a fast, pre-emptive multitasking, multithreaded, 3D and video capable GUI OS with built-in Internet access and so on. It booted to the desktop in about 5 seconds. But there were few apps, and Microsoft sabotaged the only hardware maker to bundle it.
This stuff _can_ be done better: smaller, faster, simpler, cleaner. But you can't have that and still have compatibility with 25y worth of DOS apps or 40y worth of Unix apps.
So nobody used it and it died. And now all we have is bloatware, but everyone points at how shiny it is and if you give it a few billion kB of RAM and Flash storage, it actually starts fairly quickly and you only need to apply a few hundred security fixes a year. We are left with junk reimplemented on a basis of more junk and because it's all anyone knows they think it's the best it could be.