Caves are sunless places, dark and foreboding, filthy dirty and dangerous.
The relationship between people and caves is often a shaky one, marked with misconceptions and fear. It's no wonder that people are often reluctant to enter these mysterious realms. After going in a little way, the king apparently thought better of the idea, and decided to exercise some sovereign privilege. Having options available to him that most modern cavers don't, Francois sent two prisoners from his dungeon to explore it for him. Upon their successful return, the king spared their lives.