People generally want to program to accomplish goals, and they want to minimize the amount of setup time and yak-shaving needed to start working on those goals.

Nix does solve a lot of complex problems and gives you a lot of control over your dependencies. But if the complexity to start using Nix for your project is too high, then you're going to opt for a less powerful solution that lets you get stuff done.

I say this as someone who really loves Nix and the power it provides -- the UX is a huge challenge for adoption. It's better to confront that fact if we want Nix to succeed.