Right, it totally makes sense to use your existing build system if your project is a mature C/C++ project, and especially if your project is something like systemd, which is the backbone of the vast majority of linux installations. That’s a special case, I would argue, whereas 1% of rust programs that import any external code can be built out of the box with cmake/ninja/meson and 99% of them rely on cargo and likely a build.rs.