That would be enough control, right?
There's no hard technical reason for that. It's mostly that PyPI only want to trust certain issuers who they think will look after their signing keys responsibly.
I disagree with your assessment that provisioning API tokens is better than being able to authenticate with a JWT. It makes managing credentials in an organisation much easier as far fewer people need access to the signing key compared to who would need access to the API token. Using asymmetric keys also means there's less opportunity for keys to be leaked.
If you work in a large organization that has the ability to maintain a PKI for OIDC, you should open an issue on PyPI discussing its possible inclusion as a supported provider. The docs[1] explain the process and requirements.
As long as those packages get digital attestation, perhaps attested by PyPI itself post-upload or from a well-known user provided key similar to how GPG worked but managed by PyPI this time.
Surely you see how this is creating two classes of packages, where the favored one requires you use a blessed 3rd party?
The strongest possible version of this is that projects that do provide attestations will be checked by installers for changes in identity (or regression in attestations). In other words, this feature will only affect packages that opt to provide attestations. And even that is uncertain, since Python packaging is devolved and neither I (nor anybody else involved in this effort) has literally any ability to force installers to do anything.