I think they're just using Node as a JavaScript runtime. It offers a bunch of libraries, an interpreter (V8), a package manager and so on. Additionally, it's more and more likely to be in your package manager, so it's easy to install.

Basically, it's like having an NLP library for Python--it's not just for the language but for the whole ecosystem. The difference is that JavaScript as a language does not provide stuff like modules, so you have to get that from somewhere else, in this case Node.

1. New framework written

2. Wheels reinvented to fit on new framework

3. Framework develops an "ecosystem"

4. Framework grows to support ecosystem

5. Framework criticized as old and crufty. Repeat 1 with new framework.

An NLP API server might be a good fit. It wouldn't be awful to be able to throw lots of data from web scrapers, twitter streaming api, etc to a node server to do NLP. It would also be nice to use for any other node project where you'd benefit from NLP along with whatever else you're doing.

It would be more accurate to say "natural language processing in Javascript". Javascript has a few NLP libraries but afaik there is no clear go-to library yet.

Natural is great for example for analyse a tweet stream... Is very useful for me.