They made the decision. It could be done but you have no idea of availability on United. It's a process to get all those people rerouted.

Plane going back the next day causes a ripple effect on the schedule as well. Because normally it would go to Newark and fly back within a few short hours with ANOTHER crew. Now you need this same crew to get its mandatory rest period, you need to scramble to get them accommodations and then you fly the plane back empty later than scheduled.

Almost all of the flights in the air turned around and went back where they came from btw. Only a few continued on and those were probably already past the point of being able to return