This is a very clever platform play. If you make Siri / your mac the central access point for all AI related workflows and make models interchangeable, then Apple has a huge weapon in the AI race.
I don't disagree, but I do feel the need to point out this was not Apple's plan A. Luckily for them they have so many tools and options at their disposal, that they are able to massively fail at developing their own models and still end up in a good position.
Handle the query on device. If the device cannot handle the query, push the query to Private Cloud, If Private Cloud cannot handle the query, push the query to a third party of the users choosing.
Which is pretty much the same as what they announced a few years ago.
Apple underestimated the amount of time and work needed to get to work and really the only bit that I think changed is that Private Cloud (and possibly the on device model) is a white label Google model rather than being developed in-house by Apple.