Tottenham Hale is reached in 35 minutes from/to London Stansted - this gives direct connections on to the tube network.
Not everyone wishes to go to Liverpool Street/Central London/Victoria
Stansted has a much better coach network in to London (Stratford/Victoria) - Gatwick has no real coach feed in to London and relies on the direct rail link.
Found this out to my cost when I arrived at Gatwick a few weeks ago when the train strike was on - people had no means of leaving or arriving at Gatwick other than by car, taxi (3 hour queues) or local bus.