Automatically downloading AI models into disk space with no user-facing way to turn it off is especially hostile considering Apple as vendor of both the OS and the hardware is the same entity that overcharges for non-upgradable SSD storage in their machines.
Like it or not, Siri is one of the features of macOS and has been for a long time. It's not just some arbitrary AI model that Apple decided to store on your disk.
They'll rent you more iCloud space when you fill up the SSD. That's good, holistic customer service.