phloo This kind of discussion has been had a thousand times before, and let me assure you, the Flarum team is not closing its ears to it.
The part that may make some users uncomfortable is that Flarum is focused on being a framework for a community platform. The core software is intended to be small and minimal, to be extended by customizations on top. If you need more evidence of this, look at the extensions that Flarum itself bundles, features that would be considered essential to running a forum like Tags (discussion organization) and Lock (moderator actions) are added on top of the framework.
Such would occur for any user management solution, whether it was Flarum created or not. At the moment, the fastest solution for this would be that the community creates such an extension. It would be free of the constraints Flarum has for its extensions, such as appealing to a broad audience of sites and yet still be nonessential for Flarum itself to work.
Flarum is focused at the moment on getting to stable, and that focus is on getting the extension API to a stable point. Sidelining that work to create a user management solution would be a waste of time for Flarum to create itself, it would have to be rewritten with changes in the extension API that are planned for the next few releases, and it would delay those releases as well.
This is what luceos means about it creating more work. The goal here is Flarum at stable. If Flarum at stable lacks a user management solution, that can be fixed after stable with much more confidence than it can be done now. And if the community provides a better solution in the meantime, all the better.