| We will probably never know the real reason(s) why cats like high places, but here are some theories:
Height can indirectly be a sign of status. If there are multiple cats in a household, the cat who controls the best perches is generally the most dominant. The highest cat is literally the 'top cat.'
The height gives the cat a better observation point. From that location, the cat can survey his 'realm' and be more aware of activities of people and other pets. In the wild, a higher place may serve as concealed site from which to hunt.
Living in the Northwoods, I think one of the reasons my cats like the top perch on the cat tree is that the tree is located near a heat register, and the top perch is the warmest spot. The tops of refrigerators also tend to be warm.
If a cat is anxious or afraid, a high perch may get him farther away from the cause of his anxiety (e.g.; a dog).
Why your particular cat seeks higher places may be a combination of these theories, or something only he will ever know.