Why? Because it's cheaper to roll the dice and pay less for medical services out of pocket. He's a smartie.
Alito then flipped the tables, saying that the mandate will require young, healthy people to pay more per year for insurance than they would pay for health care out-of-pocket, thus forcing them "to subsidize services that will be received by somebody else."
"If you're going to have insurance, that's how insurance works," Justice Ruth Bader Ginsburg argued back, in the first of the four-justice liberal bloc's attempts to shore up the government's case.
The entire point of insurance is not just to pay for routine healthcare, but to have a means of paying for healthcare if and when something really serious and prohibitively expensive occurs. This can happen to anyone irrespective of age or health. Meanwhile, as Justice Ginsburg argued, the premiums that aren't used for immediate care available in the pool for people who need it.
Adding... Yesterday's arguments didn't go very well for the ACA and the administration.