I feel like I understand nothing about the nix language

Pure lazy unityped lambda calculus, basically a lazy lisp with records instead of lists. Or a pure, lazy, lua.

Pure is important because reproducibility, lazy is important to not have to evaluate all of nixpkgs before you can build anything, lambda calculus well it needs to be turing complete, support things like functions in in some way though TC is only used very, very very deep down in the system. They literally use the y-combinator to do recursion, like when bootstrapping stdenv.

The syntax is unintuitive, yes, but aside from the semicolon cancer actually not that bad. My biggest gripe with the language is it not having a proper type system, like you put a list where a string is expected or the other way around and you get five screenfuls of backtrace through the whole evaluation stack and due to laziness the actual location of the error might not even be in there.

A replacement is actually already in the pipeline.