On The March
During the Dark Ages, traveling in the dark was extremely difficult, especially if you were seeking to win battles or claim new territory. Logistically, moving an army across a nation has always been difficult, but it’s much more so when they don’t have any modern technology. You would almost certainly lose a few soldiers to the elements before reaching the conflict.
Furthermore, after a successful campaign, you’d have to return all of your gains to where you came from. It would also have been more difficult to defend against robbers or other attackers on the road back because of the loss of a few fighters. This photo appears to show the Normans or the French army, not the Vikings.