If this were an "insurance" market, when you get diagnosed with a problem (cancer, say), the old insurance A would have to pay for the cancer treatment, and kee

If this were an "insurance" market, when you get diagnosed with a problem (cancer, say), the old insurance A would have to pay for the cancer treatment, and keep paying even if you leave the insurer. Any "new" conditions would be covered by your new insurer B (or not covered, if you didn't get new insurance), and insurer B would have the right to refuse to pay for pre-existing conditions because those would be covered by your old insurance A. But that isn't to say that if we had "insurance" life would be altogether better. Insurers would increase the premiums of people who beat cancer, because cancer has a habit of coming back. Quite likely anybody who beat cancer would be unable to afford insurance in the future.