Here in the US, we'd say it's because they wanted to be classified as a fancy-pants "gated community." It's got a gate, so it must be fancy and secure!
Near our house is a property that's got a huge, 1-acre flat lawn...and a gate on their driveway. No fence. Anyone could just drive on the grass around the gate if they wanted to. It's not going to stop anyone they'd want it to stop.