It is used as package manager often enough -- stick "git clone", or ExternalProject into the CMakefile and you have the (bad) equivalent of "pip install" for C++.

For example, I mentioned "kitware superbuild" above. It describes itself [0] as:

> It is basically a poor man’s package manager that you make consistently work across your target build platforms

[0] https://blog.kitware.com/cmake-superbuilds-git-submodules/