Well, sometimes it's because you already boarded and started to taxi and there are so many planes on the ground that there are no gates open to get back to the

Well, sometimes it's because you already boarded and started to taxi and there are so many planes on the ground that there are no gates open to get back to the terminal so you spend hours on the plane waiting for a slot to open so you can get off, meanwhile the galley runs out of food/drink and the toilets fill up. Then when you finally get into the terminal, it's chaos, no one knows when planes will be flying again so you're not sure if you should stay there or try to get a hotel (which fill up quickly from all of the stranded travelers)