I know this is a completely uneducated question from someone who only flies airlines as a pax, but I've always wondered why ATC clears folks to taxi if the know they can't accommodate a timely takeoff (the example of the closed runway due to a burst tire excepted, of course)?
As a customer, I'd much rather wait at the gate knowing that when you get a pushback it'll be a real go than sit out on a taxiway for several hours.