How does this solve the problem of both governments and corporations wanting to implement this in ways that allow them to hoard datasets?

As it stands, the government in the US uses an identity verification vendor that forces you to upload videos of multiple angles of your face, enough data for facial recognition and to build 3D models, along with pictures of your ID.

I use Tor, so I get to see how age verification is implemented all over the world. By large, the process almost always includes using your government issued ID and live pictures/videos of your face.

There are zero incentives to implement zero knowledge proofs like this, and billions of dollars of incentives to use age verification as an opportunity to collect population-wide datasets of people's faces in high resolution and 3D. That data is valuable, especially for governments and companies that want to implement accurate facial recognition and who have AI models to train.

Nothing "solves" the problem of governments wanting to collect data on you. Governments will likely always want this, until we start caring about the issue enough to elect ones that don't.

The important point is that such invasive approaches are not required; clearly, however people already authenticate with government agencies for getting a driver's licence or passport would suffice. I think it's the responsibility of knowledgeable tech people to advocate for this.

I suspect that this is going to happen one way or another anyways. You already have to scan your face at the airport here.