Obviously this assumes you arrive and both lines appear to be equal and it’s somewhat busy.

Why? It’s all about the space beyond the speaker/ordering spot and before the merge point. The inside lane will be blocked by both the car who was in front of them and by the car from the outside lane. In the meantime, the outside car is able to order while the inside lane car is still stuck waiting for the car in front of them to advance far enough so the car behind them can order. Once the inside car has ordered, it’s likely the car on the outside has ordered and nudged their way ahead so the inside car can’t advance ahead of them. Rinse and repeat.