why does npm init actually initialize a grunt project?

I'm trying very hard to understand the Node ecosystem and how npm and its packages work together and I find it very odd that npm init initializes a "grunt project" and adds a package.json file to your directory.

Since the node package manager manages many different "packages", I would expect something more like npm grunt init

Can anyone fill me in on what's going on here and what makes grunt so special that it gets to be the main npm init command?

All npm init does is give you prompts (see below) to create a package.json, there's nothing grunt-related that comes with it.

name: (test) 
version: (0.0.0) 
description:
entry point: (index.js) 
test command: 
git repository: 
keywords: 
author: 
license: (BSD) 

Grunt can certainly (and probably should be) installed with npm but it's definitely not part of initializing your package.json.

You can read more about package.json here.