That's only true you succumb to the hardcore Nix fanatics and follow their recommended "declarative" way. However, Nix, as a package manager, is perfectly usable - and accessible - with the imperative way, without having to subscribe to their religion and learn their language and terminology.

In the imperative path, Nix is as easy to use as any other package manager, yet it still retains many of the unique Nix features such as versioned packaged, instant rollback, non-root user-based installs etc.

It's a shame because Nix is actually really cool and very easy to use if used this way - and especially useful on immutable distros, locked-down systems or distros which have a limited number of packages - but unfortunately, most people are missing out because the fanatics keep preaching the declarative way as if it's the only option out there.