(This probably says more about how hard it is to build C++ than anything else)
That's probably true, but I wouldn't be surprised if something like windows doesn't have a README file. And it does have build instructions they may well be in some wiki separated from the source code.
Video games build systems are a thing onto themselves even taking the c++ issues out of the equation.
Hell even comparatively simole microservices in modern CRUD apps have resorted to docker to do away with pains of rebuilding stuff.