The answer – as journalists used to know by heart – is not for the sake of health but for the lust for money. Which you can make a great deal of when you can force almost everyone to buy what you're "selling."
Health insurance and car insurance being the prior examples – and precedents.
oth used to be on offer for those who wished to freely buy them. When that was the case, many people didn't – for many reasons but all of them coming down to a calculation that it wasn't worth it, to them. The cost of the insurance vs. the cost of not buying it. The result of this option was that the cost of insurance was less – for everyone – precisely because of the pressure on the sellers of insurance to offer it at prices low enough to make enough people want to buy it.
Better to force everyone to buy it.