I think this belief is based on faulty assumptions, such as survivorship bias.
C++ became popular largely because it started off by extending C with the introduction of important features that the developer community wanted to use. The popularity of C++ over C attests how much developers wanted to add features to C.
C++ also started being used over C in domains where it was not an excellent fit, such as embedded programming, because the C community prefered to deal with C++'s higher cognitive load as an acceptable tradeoff to leverage important features missing from C.
The success of projects such as Rust and even Zig, Nim also comes at the expense of C's inability to improve the developer experience.
Not to mention the fact that some projects are still developed in C because of a mix of inertia and lack of framework support.
So to claim that the C programmers do not want change, first you need to ignore the vast majority that do want but already dropped C in favor of languages that weren't frozen in time.
It's also unbelievable to claim that a language that precedes the concept of developer experience represents the apex of language design. This belief lands somewhere between Stockholm syndrome and being mentally constrained to not look beyond a tool.
