As I said, it IS Vegas - the ultimate leisure destination. Some passengers to Vegas don't necessarily care when they get there, as long as they get there.

A very late flight to Vegas does have its advantages - you can get a full day of work in MEM, eat a nice meal, and still make the flight without rushing. You'd also arrive in Vegas with enough time to rest up for a mid-morning meeting or convention (or make a bee line to the craps tables - they don't shut down the casinos in Vegas just because it's after Midnight).