What's the point of implementing something like this completely in Javascript? Isn't this a good example of something that should be developed in a lower-level, faster language?
This and other JS CLI libraries are typically used by JS projects that have tooling. Like when create-react-app scaffolds a project and asks you questions to customize it, etc. it's using libraries like this one. For a JS project it's just an easy npm install away as a dependency, and you know your users will have nodejs anyways.
Speed rarely matters for imperative user-facing tools. You're going to be waiting for a user to type and respond far, far longer than making some system calls to write to the shell.
Ink is a more interesting and maintained library to consider though: https://github.com/vadimdemedes/ink It lets you write react-like apps that output to the terminal instead of HTML.