My experience lies in consumer events, and there are two simple reasons why booth babes are used. 1.) Visitors like them. 2.) Exhibitors themselves like them. And reason 2 is the biggest. While number 1 would be enough to justify it in either case, most people base it purely on "hey, I love seeing booth babes, clearly they're a good idea". And it's hard to argue with the success they have.
Both these groups of people are happy to be, and be perceived as, creepy.