Sometimes a snake will seek areas of the enclosure that are more or less humid based on their needs. So for example, if you have damp sphagnum moss on one side and nothing/dry on the other side and the snake needs moisture, he will curl up with the damp sphagnum. However! Ball pythons are known to sacrifice comfort/heat/humidity for a good hide, so I like to put moist sphagnum on both side of the tank for balanced humidity, and to give my babies a chance to stay humid no matter what side of the tank they are on. If you have a hide on only one side, your buddy may stay there because he feels safest, even if he's dry/dehydrated/cool.