When the easterly departures to the South west were changed in the (much noisier) 1970s to route down the Mole valley I gave some technical assistance to our local anti-noise committee.
We were particularly puzzled by one rather tortuous path until we discovered that the chairman of the Noise Advisory Council lived at Epsom.
Strangely enough, the SID seemed to route around Epsom.
Never underestimate the power of major bureaucrats to influence your life.