Hmmm.
In Greenham you had:
a huge runway, rendered surplus by the end of the Cold War, on the right side of London, yards from an existing railway line, and a sneeze away from the M4, close by a town that already needed a by-pass spur down from the M4.
Option 1: Use the base as the basis of the much needed extra London airport, upgrading the rail link to Newbury racecourse and building the bypass to the East of Newbury (the !!!!ty side, though full of rich folk's houses) going via the new London-Newbury airport.
Option 2: Tear up the runway, build the bypass through the more unspoiled, more attractive country to the West of Newbers, and leave yourself with LGW still stuck in the most inaccessible part of London's environs and with LHR groaning at the seams.
And which did we choose?
London-Lyneham International, anyone?