Louisville is a better choice over Vegas for a lot of reasons. More centrally located, more local flavor in restaurants and although the Executive West is an older hotel, it means a LOT cheaper rooms. This will allow people to spend more on beer and gambling and No Doz tablets as part of the budget. Derby has been successful in part to some of these reasons. Cheaper expenses mean more people will make the trip and "contribute" to the overall purse of the event.
Oh and for PROG8R, since prostitution is legal in Nevada you pay more due to regulations and taxes imposed. So you win-win by having cheaper hookers in KY too! There you go! Git R Dun.