Old people are expensive. If the people on Medicare were as healthy as the average 50-year-old, it would basically solve Medicare's long-term funding problem. If it cost, say, $100K every 10 years, it'd be worthwhile to give it to everyone for free.

Edit: checked numbers. There are about 40 million Americans 65 or older, and Medicare spends about $600 billion/year, for average annual spending of $15K each.