It's LACK OF INTEREST.
I am sure you know the mechanics of how it works but if it not here it goes:
Men are biologically wired to be attracted to good looking young women. Strip clubs have a reasonable supply of these (although strippers are not as good looking on average as the popular culture would lead you to beleive).
Women, on the other hand, are attracted to confident men who exude that they can HAVE whatever woman they want. Once a man walks through the doors of strip a club he stating in a pretty bold voice that he is there to PAY FOR PUSSY. Hence he has "lack of confidence" written all over him. (If he was confident he could get any pussy he wanted he would be in a singles bar picking up women for FREE).
Thus when a customer asks the stripper to see him outside the club for free, chances are she is not attracted to him. Now honest girls would just say so, but strippers are not exactly reknowed for their morals, so what they do is, instead, lie and lead on the customer in hopes that he will continue to provide them with MONEY.
(Sometimes strippers will rationalize this in their own minds as follows: well he is just trying to use me for sex anyway, so it is fair for me to just use him for money. Other popular rationalizations are: If I don't take this sucker's money someone else is just going to; If I don't take his money he is just waste it all on other strippers anyways.)