Thought the purpose was to bring Canadian oil down through America for refining, thus eliminating the need to truck or rail vast amounts of crude on less safe transport, such as this one which went horribly wrong?
It still is, but keep in mind that North Dakota is the second largest oil producer in the nation, and that that has developed over the last five years or so (passing Louisiana, California, and Alaska). Pipeline capacity isn't close to keeping up.
The type of crude matters, too, and the heavy Athabascan crude is better suited as a feedstock for refineries geared toward that type of feedstock.
The oil from the Bakken/Three Forks is a light, sweet crude which is more suitable as feedstock for refineries which have traditionally refined Arab Light or North Sea (Brent) oil. Those refineries are on the coasts, and the market is there (very little pipeline capacity headed in that direction, so rail has proven to be the expedient and cheaper alternative).
That said, who in their right mind would leave a train of cars loaded with crude oil and pressurized gas unattended? It'd be a terrorist's wet dream.