@NorthXNorthWest
You are not special, we all carry health risks, some you can’t control, like genetics or random chance. You might still end up with something like dementia or cancer. But there is a lot you can influence through how you live and manage your health, which can affect when illness shows up, how severe it becomes, and how much strain it puts on the NHS. That’s not about blame, it’s just reality or scarce resources, and why personal responsibility has to be part of the conversation.
Another point is that being fit and healthy improves your chances of harsh treatments being tolerable and effective. Take one of the many cancers that doesn't have "lifestyle" causes. Being fit and healthy may well improve your tolerance of the chemotherapy and other drugs, may mean that you can tolerate a stronger dose to hit the cancer quicker and stronger, or even a "healthy" gut system may make some of the drugs more effective due to absorption etc.
My DH has a cancer with no known causes - his haematologist has often told him it is pure "luck" as to who gets it and who doesn't. She's been regularly amazed at how well his body responds to the treatment. His first course of chemotherapy should have been "at least" six rounds and he was started on the highest level of drugs to "hit it hard". The blood "markers" for his cancer halved after just the first round, then halved again after the second round and were negligible/trivial after the third round, so they didn't do rounds 4 to 6. Haematolologist said she'd never seen anything like it. And that was after they'd halved the chemo dose for the second and third rounds. DH was "super" fit, had always eaten healthily, never smoked nor drugs, very moderate alcohol (occasional, not even weekly), not overweight, plenty of exercise (walking, cycling, swimming, skiing, golf, squash etc). He was told that the first chemo session would "probably" last 18 months before the next major treatment cycle was needed (it's incurable, but treatable), but the very lose "maintenance" dose he's been on, has now lasted 7 years and is still keeping it under control, which again, the haematologist has never heard of before!
I do think people need to take their fitness and health more seriously. It really isn't just that so many diseases/illnesses are caused by poor lifestyle choices, it's that a healthier body can respond better to treatments for all the other diseases that don't have known causes.