Do they not? Many phone functions are already available through voice assistants, and have been for a very long time, and yet the vast majority of people still prefer to use them with the UI. Clicking on the weather icon is much easier than asking a chatbot "what's the weather like?"
>>flexag+(OP)
My elderly mother has an essential tremor (though only in one hand now due to successful ultrasound treatment!) and she would still rather suffer through all her errors with a touch interface than use voice commands.