Why do people jump so eagerly to this assumption about the wishes of the dead being unimportant? We honor wishes of the living concerning the exterior world bey

Why do people jump so eagerly to this assumption about the wishes of the dead being unimportant? We honor wishes of the living concerning the exterior world beyond the mere facts about their brain state (e.g., someone can justly want to climb Mount Everest or set a world record, and not just believe they have). Continuing to respest their reasonable wishes after they die is not fundamentally different, e.g., not desecrating their bodies, even if they don't have family who would be upset.