It failed because it turned out not to be usable, in practice. Getting something equally ambitious and also usable was a research project. Blaming ISO politics is a way to avoid need to understand unpleasant technical details.
You wish C++ were becoming a niche language, but in fact its usage is still growing by leaps and bounds, as it has been continually since C++11 came out. Every week more people pick up C++ than the whole population now employed coding that other language. That will be true next year, too.
You wish C++ were as widely used across the whole OS stack as back in its glory 1990's days.
The fact is that it has become a niche language for GPGPU programing, OS drivers and embedded standards like AUTOSAR, everywhere else another language takes the crown jewels, iOS, Android, macOS, ChromeOS, Windows Apps, Web, cloud computing infrastructure,... where is your growing C++?
So much that Apple and Google are now rather focusing on their own languages, with C++17 being good enough for their own purposes, hence why clang is trailing its ISO C++20 compliance.
When everyone brings their own agenda to the table regarding implementation details it is politics, not only concepts, contracts, ABI breaks (god forbid!), reflection, networking, graphics,...., definitly politics.
But hey, it is growing on GPGPU, HPC, Machine Learning libraries for Python, LLVM/GCC implementation language, so there is that.
When one works with teams our options don't work in isolation.
As for concepts working in preventing compiler vomit, there is still plenty of work to do in 2021.