Companies with strong distribution have an option to be the "last" player in a market and simply force their way in. If Apply makes a "default" LLM which is as good or better than all premium LLM options... then you would obviously choose to use that over paying for a ChatGPT subscription. Apple could probably upcharge the phone by $200 for this privilege. Alternatively, they may do what they did with search and just get paid not to add an LLM chat functionality.