There are simply too many bad actors in this day and age, and I believe to prevent foul play or not acting appropriately if there is a dire situation, the eldest will always be of most sound-mind to protect their parent’s inner wants or needs.
I don't know if I still remember what genuine happiness feels like because my mind has grown so accustomed to being unwell that whenever I catch even the faintest glimpse of hope, it stabs me in the back and drags me by the hair snarling, "where do you think you're going?"