Here's what author says.

With Typescript, you get the full power of programming — the ability to easily factor out variables, to connect and abstract functionality, to reuse code, to write tests. But you don't need to learn a new language. You don't need to find documentation (it's right there in your editor, if you have LSP set up). You don't need to try to make sense of a page of Nix traceback (type errors will show you where you went wrong much earlier and more precisely).

I personally agree with this. Learning a new language that is poorly documented is pretty difficult. (I still learn Nix though since I think it's fun)

If this state will persist, Nix will end up being like haskell with exclusive community, which leads fhe language itself to death.