C++ is used for large, very, very, very, very complex problems. Language-specific build systems always like to assume all the world is their language. But not all my world is C++, just 99% and that last 1% is all kinds of weird, screwy things that require a very complex build system. CMake is up to the task, in part because CMake is used for building more than C++ and so they've thought a little bit about the issues I have.
Anyone who says CMake and C++ are complex languages is utterly completely wrong. Sure, by comparison to something better designed, they're a little more complex, but we're only talking a little bit. Meanwhile, I have tens of millions of lines of code to deal with. My real complexity isn't the language, it's my code and that is far greater than all these little complaints people have about the language complexity.