An employee

I work at BK, which prides itself on great customer service. Why then is the drive-thru cashier not allowed to tell a customer sitting at the speaker that she will be right with them? Yes, we are told to never say this to a customer under any circumstances. Many times at night we have a car with a huge order, one person in the kitchen, one person up front. Another car pulls to the speaker while we are filling the order of the first car. The second customer waits, waits, asks "Hello? Hello?" Yet we are not supposed to tell them that we are aware of their existance. I think this is a hell of alot more rude than "I will be right with you."