There was this one man who was hit with so much radiation that his skin fell off his body and he was melting from the inside out. The amount he received was meant to kill him in days, but the hospital kept him alive for so long that whenever he was conscious, he'd beg for them to just let him die— but they did not. They had to save him (his family was adamant, I think) though everyone knew he was a dead man. Rather than days, I believe he lived for 3 months or something like that, and while plenty of that time Im sure he was in a medically induced coma— they kept waking him up. he kept begging. And he didn't have a way to end his own life— so he laid there in puddles of his own blood until the hospitals could do nothing more.
Similarly, I recently watched a video about Agent Orange on YT, and one of the kids they showed had a severe heart defect that was killing him. He needed a transplant. He could not sleep lying down because it hurt too much. He was perpetually tired— and the entire time his family was being interviewed, his head lolled from one side to another, and he was so exhausted that he could not even cry. He wanted to DIE. And inevitably, he did.
Re: pain, this is omething my mother endured, as well— she had such chronic pain that she had to use a walker in her own home, and could not stand up and get food more than once a day because the pain was excruciating. She'd spend hours lying in bed waiting for the energy, the desire, or something like that to get up and get to the bathroom. Sitting on the toilet was so terrible she'd scream in pain— and all the while, she was grieving my father and waiting until she felt I was well enough mentally so she could try to kill herself. She wanted to die her whole life. She told me repeatedly, when I was younger, that all that kept her from killing herself was me, and my father.
All of this sticks with me because I would hope I could ctb long before i got to that point. I can't bear losing my eyesight as I am, let alone suffering extended pain day in and day out on top of my already severe depression.
And a lot of this shit comes along with getting older, too. People get sick, develop severe illnesses or arthritis, need to have surgery and are laid up in hospital beds until they inevitably die. So, at this point the question I ask myself is, when will it become too much? And when will it become too late for me to kill myself because I won't have enough bodily autonomy or agency to do it successfully?
TL;DR: I have no clue. Maybe they feel obligated to live because they know their family depends on them. Maybe they are too bedbound or incapacitated to make that choice for themself, and they know no one will do it for them. Maybe their family continually requests life-saving treatment. Maybe the idea has never entered their head because they feel their life is worth more than their discomfort.