"Unusable" seems quite strong. It's usable for open source projects.

Sort of. It's only really usable for those who want to apply the same restrictions to their users/contributors.

Having to pay to use software commercially makes it unusable?

I'm surprised GitHub doesn't show this on the repository it just says "View License" but I guess they don't allow using AGPL when creating a repository.

They do support showing AGPL 3.0, but it has to be either in a LICENSE.txt or LICENSE.md. This project just has it in a file called LICENSE. https://help.github.com/articles/licensing-a-repository/

I noticed they stopped displaying licences on all repos recently. Everything says "view licence" now.

Why would they not allow AGPL? It's a perfectly valid free software licence.

So, the same way Adobe Photoshop is "unusable" or Oracle DB?

It's a lot to ask for a web framework, feels like, given the extreme multitude of options. Not unusable, but you're going to have a hard time getting users for an AGPL web framework.