At the risk of derailing the conversation (although Guix is a lisp so maybe not): I agree 100% but also maybe Nix's pragmatism is why it's more popular? "Pragmatism" being a programming language euphemism for "untyped hacky mess".
Why is this in past tense? Guix development is active. It's just Nix is more popular and it's understandable since it's the original idea and it's older.
Guix even has a very active, high-quality blog where maintainers detail major technical accomplishments, long-term goals, etc.: https://guix.gnu.org/en/blog/
From here it seems like they're growing and advancing well. I wish I could find ready historical data on the numbers of packages and services from, say, 4 years ago vs. today, though. I could have sworn Repology used to show year over year stuff but I can't find it now.