Question

Why was the 21st amendment to the U.S. Constitution necessary?

Answer 1

It repealed the Prohibition set by the 18th amendment. It didnt work out the way they wanted because the alcohol still got to the people. The widespread disillusionment led to Congress ratifying the 21st amendment.

Answer 2

it repealed the Eighteenth Amendment which had mandated nationwide Prohibition on alcohol, and obviously that's not the case now days.