Part of this is about making sure people are available at last minute notification. If you're in transit from Sydney, Australia to London, UK, you're out of action for 30+ hours plus the time to get over jet lag.
I am not buying that, People sleep and do morning routine for 10+ hours and on top of that they have personal life and weekends, you won't ask them to stop doing that so they will be available for you at last minute notification.