One obvious problem in ordering the banks to spin off their prop-desk operations is that many transactions that might be characterized that way have essential value.
Unlike a restaurant, where customers choose a meal by ordering a meal, at restaurant Med some higher force gives an unfortunate person an undifferentiated and undiagnosed problem that needs and deserves an answer.
This margin depends on the size and speed of an aircraft, and re-ordering the queue can minimise the delay before all the planes get into the air (mathematicians call this the departure problem).