I wrote up why we selected CUE here, with links to explanations from Marcel who explains it better than I: https://holos.run/blog/why-cue-for-configuration/
These comments in particular reminded me of Marcel's video linked at the bottom of that article, where he talks about the history of CUE in the context of configuration languages at Google: https://www.youtube.com/watch?v=jSRXobu1jHk