I think the cost of running these models is still astronomical, and unlike ms and google apple just doesnt really have cloud compute at their scale. So I could imagine they might run this as a premium service first to build hype, and then figure out bringing it down in cost over time.
A bit like the vision pro, its a premium product now, but I could imagine 3-6 years down the line it will cost around an ipad pro. Apple is really good at scaling things once they see the market. But suddenly switching everyone to a gpt-3.5 for siri overnight would be a humongous cost (I think).