Why would a source of signal that has aligned incentives for all three major parties (individual, manufacturer, and insurance company) not be selected for by the market?

It's not as if people are buying meteor insurance here. Automotive accidents are frequent enough to where if a policy provider fails to cover damage that really is in-policy they'll be sued, regulated, and shamed.

Even more so, since Tesla has a financial incentive to ensure that these benefits really do accrue to the driver.