I can't help but wonder if developers are simply off-put by the complexity of the language itself.
Way back in 1989 I was fortunate enough to get Borland's C/C++ compiler, the K&R C book, and Stroustrup's C++ book - which, at the time, was about the same size as the K&R C book. The C++ language was relatively simple to learn at that time: no STL, no odd pointer types, no template metaprogramming, etc.
Fast-forward to 1997 and I'm listening to a talk about C++ compilers and hear that templates are now a Turing-complete language, and how the compiler developers used the template language to coerce the compiler into printing out the prime numbers.
Fast forward again to 2022 (with trips to Java, Kotlin, Scala, and Haskell in between) and I've got a project that requires JNI and Python bindings to a core C engine. Great, I'll use C++! I proceed to start searching for containers/constructs and realize that at least 50% of the C++ language and standard library is unreadable to me. I only have a guess as to what a `shared_ptr` or `unique_ptr` type is, and I certainly don't know when to use them, and concepts/traits outlined in the STL documentation seem to be some sort of generalizations that the STL might provide default implementations for, but might not? What exactly is the syntax and/or type of a lambda function and how do they interact with C function pointers? etc., etc.
I get the sense that C++'s evolution has been driven by esoteric corner cases that a handful of developers have encountered and the language & STL design has been driven by those cases. I'm still surprised by how many problems I can easily address in something like Scala or Haskell that C++ simply does not provide the facilities to express easily.