The fundamental problem with health insurance is that most insured events are not well-defined points in time like other forms of insurance (theft, death, accident, fire, etc.) but spread out over time, e.g. you hurt your back, a few weeks later you relapse and it becomes chronic; it's often hard to follow the series of causes and effects. It it were, we could force insurance companies to cover costs for all treatments related to some illness, no matter how long it lasts, e.g. you get cancer under some plan, you get treated even if it takes 10 years. This would make health insurance just as simple as other forms of insurance. "Pre-existing conditions" wouldn't even be relevant.