To oversimplify, that's why prohibition 1.0 had to be done via constitutional amendment; but since then, we had the Wickard v. Filburn ruling, which made virtually everything regulatable under the Commerce Clause with its extremely broad interpretation of the phrase "interstate commerce".

In Wickard v. Filburn, a farmer grew grain on his farm. He did not sell this grain, whether across state lines or otherwise; he merely fed it to his own livestock on the same farm. SCOTUS ruled that this could be regulated via the Commerce Clause because, if he grew his own grain, he could be expected to buy less grain on the open market, which could indirectly affect interstate commerce. By that logic, virtually anything can affect interstate commerce, and be regulated as such.