NixOS is the most daunting Linux distribution ever, and all the people I know that use it are extremely smart. You need to develop a really good mental model of how this complicated web of Nix scripts works, to create packages.
I think using nix for personal projects helps build your mental model a lot more. Once you take the time to build a package manually alot of it clicks.
As a user of nixos/nix if you're not building packages it's great. Nixos is quite declarative for most settings. The main issue is just figuring out what options exist...
We not-so-smart developers tend to go for the simplest solution possible (but usually, no simpler).
I believe it's not very weird if someone says "I messed up my Arch Linux installation, and so re-installed from scratch". (Although I don't think it's common for people to re-install all the time).
Or the most ubiquitous way of deploying software from one machine to another is to build a Docker/container image. i.e. to package the built binaries of executables and libraries in such a way that they can be run portably. -- Prob'ly the most common way to build Docker images is to write a Dockerfile, which is more/less a simple sequence commands to run.
I mean.. lots of stuff involving installing/distributing/configuring packages is very hard, and conventional solutions are layers of familiar beat-things-into-shape solutions, where you don't need a deep understanding of what's going on to get things done.
Some of the implementation in Nixpkgs is complicated (like lazy fixpoint stuff), but I've also seen e.g. developers not like Nix because they don't like the idea of learning the Nix language.
The same is true of the often bashed systemd - system boot is a hard problem, it gives a correct solution over incomplete but simple ones, and thus it will be more complex. But some complexity is inherent, so we just have to deal with that. (Rust could be another example - correct manual memory management necessities some added complexity )