We have laws in the USA that regulate just how long an airline is allowed to keep pax onboard. I googled passenger rites and found this.
"As of April 2010, airlines operating flights within the U.S. may no longer keep a plane on the tarmac for more than three hours, and they will have to provide "adequate food and potable drinking water" for any delays longer than two hours. There must also be functioning lavatories onboard during the delay, as well as medical attention when necessary. (The three-hour rule is waived if safety or security is at stake, or if air traffic control reports that airport operations will be disrupted if the plane returns to the gate.) Airlines who violate this rule must pay a penalty of $27,500 per passenger.
In 2011, the DOT expanded this rule to foreign airlines operating in the U.S.; a four-hour limit on tarmac delays applies to international flights."
27k x 4-500 pax on a 747, that would be a heafty fine.