Because they don't. No booze. It's been that way forever.
Or else everybody's "last meal" would be a bottle of 151.
According to Wiki:
The last meal is a customary part of a condemned prisoner's last day. Often, the day of or before the appointed time of execution, the prisoner receives a last meal and religious rites, if they desire. In the United States, inmates generally may not ask for an alcoholic drink. Other countries have different traditions, such as the "little glass of rum" granted to the condemned in historical France in the minutes before execution; but no formal last meal as they were told of the impending executions only on the fatal morning, generally minutes before the actual event
It's a state matter, but I've never heard of any state allowing alcohol to an inmate.
Biscuits & Gravy (my own recipe), fried eggs with hot sauce, pancakes with butter and maple syrup, white milk, chocolate milk and black coffee. Nothing special, but at least it would make me happy one last time.