A lot of what makes declarative stuff nice is it comes with an implicit opinionated standard way of doing stuff. Nix tries to be way more general to the point of a whole programming language.
Where everything is closer to true configuration not declarative programming. Apt and PyPi packages in, snap package out, install it like it was an exe or put it in an app store, give it some permissions, done.
They don't introduce any new concepts and there are few intermediate extra steps, it's all more of less pretty common ideas found in any tech workflow.
Compare that with Snap packages: https://snapcraft.io/docs/python-apps
Where everything is closer to true configuration not declarative programming. Apt and PyPi packages in, snap package out, install it like it was an exe or put it in an app store, give it some permissions, done.
They don't introduce any new concepts and there are few intermediate extra steps, it's all more of less pretty common ideas found in any tech workflow.