Why is a fuel stop needed so soon after leaving Rothera for Halley?

Here's my first real documented anomaly of this mission. I started in Punta Arenas and landed in Rothera. It was a 4 hour trip.  I was able to find some search results on that at a UK site (below) to verify that. But then the flight time from Rothera to the next big base over, Halley, takes 8 hours (2X!!)-- even though the Punta Arenas to Rothera distance looks roughly the SAME DISTANCE. 


Here is the source for the mileages. 



I have to wonder why Fossil Bluff is used to refuel so SOON after leaving Rothera. I would think you could fuel up in Rothera enough to get to Halley.