I currently have an architecture where I have a whole bunch of C++ code doing computational stuff. Later (years after writing the core computational library in C++) I was asked to expose the library via a REST API. At the time I was pretty young (didn't and still don't have the necessary experience to write a web framework myself) and none of the existing C++ web frameworks seemed to work very well. So, I now have a complex architecture with a Java Spring front end that communicates to a C++ backend. Would have been a whole lot simpler all around if I could have easily used C++ for the whole thing.
Writing wrappers to interface c++ libraries with most common scripting languages is (usually) pretty easy. Probably much more so than trying to roll an entire HTTP server in C++.
If you have to roll your own, of course it is, hence why I didn't try... but if there was a mature, easy to integrate HTTP server library I would prefer to keep everything in C++ (or better yet rewrite it all in Rust, but that's a whole other can of worms).
