Most _C++_ projects are using CMake, but it has virtually no adoption among other mainstream languages, and given most open source is not C++, CMake definitely doesn't have any strong share of the open source market.
My comment was about Qt, which is a C++ project. Of course CMake doesn’t have any market share outside of C++, but in the C++ world it has become the main build tool for open source projects. Even Microsoft is now spending their time supporting CMake via both Visual Studio and vcpkg.
