Because they're legalistic, thinking dancing is a sin (which it is not) like smoking and drinking - and they are not. Remember the ol' prohibition days; the "sin" tax on alcohol and tobacco? Maybe the "dime a dance" halls had some impact on American fundamentalism?
Even we can't get a way from Pharisaical additions to the Law, hoping to gain merit with God.
It's either that or.....we can't dance very well!
