I count C++ projects in the "worst" bucket, where every project has its own build system, its own structure, own way to run tests, own way to configure features, own way to generate docs.

So if a build system works great for your mixed C++ projects, your build system is taking on the maximum complexity to deal with it, and that's the complexity I don't want in non-C++ projects.

When I work with pure-JS projects, or pure-Go projects, or pure-Rust projects, I don't need any of this. npm, go, and rust/cargo packages are uniform, and trivial to build with their built-in basic tools when they don't have C/C++ dependencies.