This is just speculation, but it’s probably just in case you need to work with or tweak someone else’s C++ code. Or it could be a case of the thinking that someone who knows C++ is technical enough for the job, while not knowing C++ would be seen as a general sign of not being techinical, regardless of whether C++ is actually going to be used or not.
There are some things where you’d want to program in C++ for speed, but I don’t know how common those are. For example, I know a guy writing a liquid simulator in C++ - any other language wouldn’t really do. Maybe C, or a lower-level language. But most people would just use a simulator that someone else wrote.