Why is Babel a monorepo?

The tool for managing the monorepo in Babel has been extracted out as Lerna

Juggling a multimodule project over multiple repos is like trying to teach a newborn baby how to ride a bike.

Babel follows a monorepo approach, all officially maintained modules are in the same repo.

This is quite taboo but let's look at the pros and cons:

Pros:

Single lint, build, test and release process.
Easy to coordinate changes across modules.
Single place to report issues.
Easier to setup a development environment.
Tests across modules are ran together which finds bugs that touch multiple modules easier.

Cons:

This is dumb! Nobody in open source does this!

React, Meteor, and Ember, among others, do this.