Gtihub approach to licence: why copy text?

Hi,
a colleague has added the appropriate licence to an item in our repo, which is available under CC-BY.

Up until now, it just said that in the Readme file.

I’m surprised to find that the GitHub approach to this is to copy the text of the licence into my repo.

Adding a license to a repository - GitHub Docs

Why not insert a reference to the licence? Most of the commonly used licences that I’m aware of that consider that to be their preferred way of being used - that’s why they provide persistent version dereferenceable identifiers.

See for example Choose a License (creativecommons.org)