>> I guess that's at least in part because of the difficulty of building safe, fast and highly-concurrent C applications (please correct me if I'm wrong).
You wrote that question in a browser mostly written in C++ language, running on an OS most likely written in C language.
OS can be actually pretty simple to make. Sometimes it's a part of a CS curriculum to make one. If it were so much easier to do it in other languages (e.g. in Rust), don't you think we would already be using them?
Writing a real one? Who's gonna write all the drivers and the myriad other things?
And the claim was not that it's "so much easier", but that it is so much easier to write it in a secure way. Which claim is true. But it's still a complex and hard program.
(And don't even get started on browsers, it's no accident that even Microsoft dropped maintaining their own browser).
The toy one can still be as highly concurrent as the the real one. The amount of drivers written for it doesn't matter.
The point is if it were much easier, then they would overtake existing ones easily, just by adding features and iterating so much faster and that is clearly not the case.
>>difficulty of building safe, fast and highly-concurrent C
This was the original claim. The answer is, there is a tonne of C code out there that is safe, fast and concurrent. Isn't it logical? We have been using C for the last 50 years to build stuff with it and there is a lot of it. There doesn't seem to be a big jump in productivity with the newer generation of low level languages, even though they have many improvements over C.
This is anecdotal, I used to do a lot of low level C and C++ development. And C++ is a much bigger language then C. And honestly I don't think I was ever more productive with it. Maybe the code looked more organized and extendable, but it took the same or larger amount of time to write it. On the other hand when I develop with Javascript or C#, I'm easily 10 times more productive then I would be with either C or C++. This is a bit of apples and oranges comparison, but what I'm trying to say is that new low level languages don't bring huge gains in productivity.
You wrote that question in a browser mostly written in C++ language, running on an OS most likely written in C language.