A Diverse Drupal Community Needs Composer
The Drupal community has been trying to come to terms with modern build tools for a while.
We have Drupal core which is managed with Composer, but we also have contrib modules and some of them want to use Composer, too.
The canonical example is Address module. It requires an external PHP library, necessitating the use of Composer to add it to the codebase.
At least, that's the thought.