CMake is not sufficiently distro-friendly to be the build system of choice on Unix, for something as important as dbus
dbus is one of the few projects having autotools and cmake build system. The dbus maintainer recently reported about issues cmake has on unix os from this point of view, see https://bugs.freedesktop.org/show_bug.cgi?id=103420#c21 for details.
dbus sources are located at https://cgit.freedesktop.org/dbus/dbus/, the cmake part is located in the cmake subdir. These notes are just my 2cent.