From my understanding these organizations don’t yet do anything. At least they do not grant a namespace unlike they do on npm. That might change though.
A key thing they do is offer finer-grained roles[1] for project and team (i.e. subteams within an org) management.
You're right that they don't provide namespaces, yet. I believe there's ongoing discussion about how to enable that, including via PEP 752 and 755.
[1]: https://docs.pypi.org/organization-accounts/roles-entities/