To be fair, many of the things you mention are self inflicted. Fair enough some people have it tough through no fault of their own, some though make choices that set them up for the lifestyle they complain about.
Often disease, disability and accidents are caused through poor lifestyle choices. Sometimes lots of little things add up and it's hard to see the true cause. I've not driven for 4 years so I'd say that's put me at a significantly less risk of car related accidents than someone that does.
You example is easily understood, but I think it is an error to think that if you have an healthy and cautious lifestyle, you won't be affected by any disability. There are many environmental factors that are outside of your control like being exposed to some nefarious substance while you were in the womb, with long term effects. And many debilitating diseases like Alzheimer, Parkinson or MS don't have a very clear cause.