This actually made me wonder if they occasionally do get picked up. There must be some reason that guys think talking to them is not a waste of time...
He didn't say they couldn't make purchasing decisions. Besides, there's still likely to be some value in being front-of-mind when people go back to their companies.
I also don't get it in sports. Why should a striptease-looking-girl give the winner the price (motorsport for example)?
I think booth babes are an expression of "I've got nothing interesting for you so I hired some babes to get your attention".