Covering Risks vs. Distributing Largesse
Politicians are already one of the main reasons why medical insurance is so expensive. Insurance is designed to cover risks but politicians are in the business of distributing largesse, especially with somebody else's money. Nothing is easier for politicians than to mandate things that insurance companies must cover, without the slightest regard for how such additional coverage will raise the cost of insurance.
If insurance covered only those things that most people are most concerned about-- the high cost of a major medical expense-- the price would be much lower than it is today, with politicians piling on mandate after mandate.