Lots of their drive thrus use a person to take the order, and at a busy drive thru this becomes a dedicated person or persons just to take orders. If they can flip it to AI then they could open more lanes and reduce staff. Problem is that a skilled person is going to be better than AI over a shitty audio system, look at how Alexa and Siri struggle even when they have an optimized reception setup than the crappy setup you have at a drive thru with the person sitting inside their car, with music on and so on.