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.

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.