Part of the reason we do that is that we want it to be based on what they would want. That's why we listen to an advance directive preferentially to just deciding what's in their best interest. Of course, the ideal advance directive might include naming a substitute decision-maker who can help walk through the different options that are presented in front of them—somebody who's trusted and chosen by the person.
On May 5th, 2022. See this statement in context.