When you try to assign access bundle within admin>attribute models, it shows only access bundles that have their own libraries, i.e. does not show access bundles that have no libraries.
Not entirely sure whether this is a bug or intended.
If intended, I think it would be good to allow to assign access bundles without a library as well. For example, if one wants to restrict the right to assign specific attributes only to a specific access bundle (specific users) that do not necessarily need a separate library.