I think you don't quite get my point, JUCE can be built whatever the lead devs / majority of devs prefers or even provide / maintain different build systems. These CMake modules are just small files setting up some variables with paths, etc. as such that other projects using CMake need to do a simple 'find_package(openFrameworks)' in order to have linker/compiler flags etc. properly set up and quickly start working with it.
I will just write that thing, issue pull request and you'll see how that works out.