Probably they know C but the project is complex enough to warrant something else. Personally I'd rather C++ not exist and it's just C and Rust, but I don't have a magic wand.
That wouldn't stop someone from knowing any C developers. It's still a common language today, and was more common when those 80s kids would have become adults and entered the industry.
As a kid in the 1980s I thought something was a bit off about K&R, kind of a discontinuity. Notably C succeeded where PL/I failed but by 1990 or so you started to see actual specs written by adults such as Common Lisp and Java where you really can start at the beginning and work to the end and not have to skip forward or read the spec twice. That discontinuity is structural though to C and also C++ and you find it in most books about C++ and in little weird anomalies like the way typedefs force the parser to have access to the symbol table.
Sure C was a huge advance in portability but C and C++ represent a transitional form between an age where you could cleanly spec a special purpose language like COBOL or FORTRAN but not quite spec a general systems programming language and one in which you could. C++, thus, piles a huge amount of complexity on top of a foundation which is almost but not quite right.
