Might work nicely for diseases that take a long time to kill you, but insurance companies have no incentive to find a cure to something that kills you quickly and cheaply.
While it's true that insurance companies use cost as a major driver for decisions, however it's not the only driver.
In the US, insurance companies compete with eachother to provide coverage for employers. Many (not all) companies want insurance that is beneficial for their employers. If you drop coverage for something an employer wants, you may lose a major customer.
