Were there lavish "last night of legal drinking" parties? Were people demanding the government reimburse them for goods they'd bought legally in good faith? Law enforcement can't possibly have gone door-to-door to every house in the US seizing booze, can they?
Prohibition in the United States was a ban on the production, importation, transportation, and sale of alcoholic beverages
This means it did not become illegal to consume alcohol, it became illegal to produce, buy, or sell it
Alcohol inside your home would still effectively be legal, in fact before the act went into effec many people stockpiled liquor and beer