Is it not better for you, the individual for the AI to reside on YOUR device than back at the Mothership where the data can be slurped and used for all manner of reasons, viz Advertising and Tracking?
If Apple deciding to keep Siri local you your iDevice is an example of control freakery then frankly, I'm all for it.
They IMHO have a different and better approach to Google/MS/Amazon. And frankly, given the slurping tendencies of the competition, I'm with Apple on this one.
Personally, I would not be seen dead talking to an AI but that is just the luddite in me. Or? Perhaps I don't want to broadcast that I'm looking for [redacted] to the people around me. I certainly don't want my searched to result in product recommendations. I'm sure it won't be long before there are divorces filed where the 'dodgy' searched are cited as reasons for getting unhitched.
IMHO, Apple are being refreshingly different here. Good on them I say.