Who said it did? Seriously.
A constitutional amendment was desired, not required. Jefferson prohibited the sale of liquor to the Indians in 1802 without an amendment.
Yeah. Sure. More desirable to spend a year getting thirty-six state legislatures PLUS Congress to sign onto a bill that Congress alone could pass in a few minutes.
Sure, Jefferson et al passed Prohibition for Indians without a Constitutional amendment ... but then what court was going to find in favor of inebriation of an unwanted underclass?
Congress knew that general Prohibition would be challenged in court by people who could get a judge to acknowledge that Congress had no such power, ergo an Amendment was needed. ...much as discussion of passing NFA talked of outright prohibition, but a prohibitive tax was enacted instead because straight prohibition was not a power granted Congress.
They've begged that question continuously for years. And every single time their bluff has been called they've folded.