If it isn't using the basking area then I would approach the problem by asking the following questions. It could be in the water because the water comes closest to keeping him at his preferred body temperature. Is there any cover over the basking area, or does the animal feel completely exposed while out of the water.
Gators use water as their security blanket.
Maybe then it would feel more secure while out of the water. Their very survival depends on them being cautious and wary. Sometime, during a quiet time, close your eyes and concentrate on putting yourself into the gators frame of thought. Think about what is important to you, what scares you and what makes you feel comfortable. If it isn't using the basking area then I would approach the problem by asking the following questions.