I haven't seen the movie, but I've read the book a couple of times.
IIRC, part of the reason that it wasn't shut down sooner was that chinook assets required to evacuate and back-haul equipment were tied up looking for Bowe Bergdahl.
Also, the original reason that site was selected was that it was accessible by road and logistical support wouldn't require transportation by chinook, but the road was very narrow and wouldn't safely accommodate anything bigger than a HUMVEE so they ended up needing the chinooks to resupply.
