Besides Apple apparently making Siri AI model agnostic, the choice to go with Google was almost certainly for practical reasons. Google is a low-risk established player that already has a long work history with Apple. Google also isn't in an existential battle to establish themselves, Gemini still amounts to just another project at Google. There is tangible non-zero risk that either OAI or Anthropic will be gone in 5 years, or will be forced to leave Apple high and dry to save themselves. There is almost no risk Google will be in either such position. And worst case scenario, Google has incredibly deep pockets should Apple pursue a "refund."