2 Kings 25:5 (ESV)

5 But the army of the Chaldeans pursued the king and overtook him in the plains of Jericho, and all his army was scattered from him.

The escape plan failed because the Chaldeans, who had well-fed soldiers, and probably also stronger horses, caught up to them. The plains of Jericho, the last place before coming to the jewel of the Jordan, is a flat area with little growth, and therefore the capture of the fleeing king was simple. His soldiers scattered in all directions.