It also doesn't have anything to do with Haskell or it looking somewhat like Haskell. I'm very comfortable in Haskell, and Nix looks awful to me. It's not that it's functional or it's declarative, it's that it's badly designed and not intuitive, making it hard to remember and therefore awkward to code in.
The majority of communication I've seen from Nix maintainers over the last few months has been about exactly this.
The submitted post is about exactly that while Nix powerful, they want more people to be able to use it without having to pay a steep penalty to learn it.