I don't understand why an ai model needs to be part of debian main.

It doesn’t need to be part of it, but it would be pretty convenient to be able to apt-get install some local AI models out of the box.

How useful will it be when all the repo models are just as out of date as the rest of the Debian packages?

Will Debian tinker with models like they do other packages?

Debian testing and backports repos are a thing.