Going back to the hi-res pics of Li'l St James.
This one probably gets most attention for the building and the smaller gazebo, and maybe for the comms equipment at the top.
What jumped out at me was that this is the only pic where you can see the tennis court.
Or, not exactly the tennis court, but the fence and lights. The berm surrounding the tennis court obscures it from view from the water.
Of course the berm would have done the same thing for the arena (or whatever it was) that they built before the tennis court.
Privacy from any curious seafarers that may have happened to get too close for comfort while an "event" was underway at the arena?
Such a strategic point on the island.
Imagine if you had such an island and had a tennis court at one of the highest points of the island, with a spectacular view to the water on all sides, why would you want to block that spectacular view with a berm?