Take the idea of having a single language for the shell and system programming. It forces you to think harder about the design of the language, so that it correctly works both as a command-line interpreter and as a compiled language. Lisp machines had that. Oberon system had that (in a graphical way, even). Forth systems had that. So it's not like we collectively didn't know. But neither Unix nor DOS/Windows even tried. Instead, they both feature shell languages that can best be described as "pathetic". Why did we have to wait until Windows 10 to have useful text selection in the CMD shell?
Or in programming languages, why is it that new languages always seem to take C and C++ as role models, while spectacularly failing to take any inspiration from Erlang, Ada, SmallTalk, Intentional Software, or Lisp? Why is XL, my own language, still the only one I know where it's easy to do multi-operator overloading, i.e. overload A+B*C, something it has been doing for at least a decade? Why are we unable to create a language that would work well both on GPUs and CPUs, or better yet, let me easily describe an application that uses both?
Or in interactive apps, why do we still not have good reactive functional frameworks for the web, similar to what Tao3D does for interactive 3D? (See http://bit.ly/1G8VOmr for my rant on that topic). Why is creating an OpenGL application getting more complex with each generation, instead of simpler? Why can a kid easily use GameMaker, but none of the Apple developer tools?
Or in operating systems, why did Linus Torvalds decide to mimick Unix and not the kind of mind-blowing operating system design ideas that were floating at the time? Like TaOS, the OS that was recompiling byte code at page-in time and could run a same program on different processor architectures during its lifetime? Or like MacOS, the original one, and its built-in graphical toolbox where, unlike X11, you could easily draw an ellipse inside a rectangle irrespective of line width? Or like GeOS and its 64K-based multitasking OS with vector fonts and GUI apps?
In summary, why is it that we always seems to ignore good ideas, but have no concerns repeating bad ones?
My theory is that inferior technology needs superior marketing, and that's how you win in the end. That's just a theory, of course ;-)