Roosevelt supported the repeal of prohibition because

The answer is: he thought that it afforded the opportunity to raise needed federal revenue and provide jobs.

The repeal of prohibition refers to the act of unbanning the sales of liquor or other intoxicating substance from the market.

Roosevelt did this during the time when United States experienced the great depression. He though that unbanning the sales would increase the government revenue from sales taxes and give him with the opportunity to raise needed federal revenue for welfare programs and provide employment in that industry,.