Freedom. The Constitution leaves healthcare to the states and people. It’s none of the fed’s business.
You're right that it's not the Fed's business… the problem is that they've redefined interstate commerce
to cover not only intrastate commerce, but non-commerce as well (there's also precedent to flat-out ignore the constitution) — they use these to justify things like the War on Drugs, which they've convinced a lot of people to think is a Good Thing [and defend it], which they use to accumulate more and more power (be it from legislation, or precedent, or 'regulation').