The key difference seems to be German private health insurance contracts are long-term affairs. Multi-year, or perhaps even lifetime? US health insurance contracts are typically a year at a time. So German companies have to reserve for costs projected to occur far in the future because they are liable for them, while US companies have no idea if their customer will still be around in 20 years.
My guess would be there's a healthy dollop of regulation pushing the German insurance market into that shape, otherwise you would probably see short-term insurers outcompeting long-term insurers since they wouldn't have to do old-age reserves and could therefore charge lower premiums. Consumers tend not to be nearly as good at rationally planning for long term expenditures as are actuaries.
My guess would be there's a healthy dollop of regulation pushing the German insurance market into that shape, otherwise you would probably see short-term insurers outcompeting long-term insurers since they wouldn't have to do old-age reserves and could therefore charge lower premiums. Consumers tend not to be nearly as good at rationally planning for long term expenditures as are actuaries.