why did crime increase under prohibition?

Demand for alcohol remained high despite prohibition. The money to be made making and selling alcohol outweighed the risk of being caught so people continued to do so, making them all criminals.

Because people wanted to drink booze.

Prohibition intended to reduce the amount of alcohol consumption in America. It failed.

Alcohol become cheaper, American consumption grew larger, in order to sell alcohol entire industries were created to make it attractive. Large music bands were funded to provide entertainment. The Jazz music industry grew large. Fine dinning, entertainment, and the introduction of the new Jazz music made going out for an evening the popular thing to do, being on the edge of legality made it more exciting and exclusive.

The profit on alcohol was small but in volume large. competition was tight, control of area expensive. Some of that expense was in influencing government officials and law enforcement.

The problem was in the creation of large influential criminals and the power they could use to influence government and continue to grow in their influence.

But the question is did crime really grow under the effect of prohibition, perhaps not , but the influence of criminals and criminal political influence grew. Add to that by definition consuming alcohol you became a criminal ... so crime increased with the changing of criminal law.

Opportunity. Prohibition was a foolish dream that if alcohol was illegal, men would become ideal husbands and much more productive workers and the whole country would be prosperous and sober and happy. The crusaders never took into account the fact that women liked to drink too, and that thousands of years of alcohol use could not be eliminated by legislation. With no legal supply, demand created a black market. Simply selling and distributing alcohol caused a huge uptick in the crime rate.

Because it created a whole new sect of crime involving the production and distribution of alcohol