Beyond old age, the vast majority of people are bad at taking care of themselves. So many people that it is not a moral issue. It is a systemic issue.
The problem is, you don’t need to take care of yourself, until you do. Society doesn’t prepare us for that. (I got to learn the hard way.)
All it takes is one accident or affliction to change this ability. Unresponsive due to a car accident, for example, or simply not having your list of information when you got rushed to the hospital. Confusion due to a high fever. A stroke due to an undiagnosed and hidden condition. Heck, simply age or winding up with a complicated health situation can do it.
In short: You really only can trust yourself if you have enough luck.