It's not just Parkinsons and care homes either. My nan had gruesome ulcers, for decades. They stank, they were agony. She became housebound, then double incontinent. She still had her marbles and sometimes was able to enjoy aspects of life but the indignity and pain and boredom really wore her down, and my poor mum who filled in for the "care" provided. When the pain became too much, she was put on morphine. She would hallucinate and get very paranoid. She was trapped in her home, and my mum felt she had no choice but to quit her part time job to care for her. It scarred my childhood and ruined my mum's life, although my mum put up with all kinds of awful behaviour with very little complaint. She did pray an awful lot.
My nan was taken into hospital a few time, eventually she stayed - for several months. For some reason the NHS decided forcibly feed her and medicate her, which was extremely upsetting to watch as she tried to fight them off. She just wanted to die, I believe. They said she was too out of it on morphine to know what she wanted or needed.
It was an utterly horrific experience and it scared me and my mum witless. Pray to God when I'm old I escape that fate. My mum, bless her, died of a brain aneurysm. Very quick. I would take my mum's sudden demise over decades of suffering with almost no quality of life, any day.
I don't know why we treat older people this way. I think there's a theory that any life is better than no life, and that we should preserve life because there's a chance people might get better, or new drugs make life worth living again. I think there should be more choice, as some people really don't want to go through that amount of pain and misery with no end in sight.