Having heard about the upcoming battle between the Philistines and the Israelites, the Amalekites were not concerned about any retribution for their actions. Their enemies were far away to the north.1 They did not know that David and his men were sent back from Aphek.
16 And when he had taken him down, behold, they were spread abroad over all the land, eating and drinking and dancing, because of all the great spoil they had taken from the land of the Philistines and from the land of Judah.