Why were people pushing for prohibition to be an amendment and not just a law?

Prohibition required a constitutional amendment, because the Federal government does not have the power to regulate intra-state commerce. The majority of states and many localities had already banned the sale of alcohol.

Explanation:

worcester v. georgia, legal case in which the u.s. supreme court on march 3, 1832, held (5–1) that the states did not have the right to impose regulations on native american land. andrew jackson refused to enforce the ruling, the decision form the basis for most subsequent indian law in the united states.

b. they tried to evict the squatters from the area.

so sorry if wrong