Affluence mainly tbh, not really much to do with greater London in it self as a lot of areas in greater London like Hayes, Ealing, Harrow, Wealdstone, Feltham, Hounslow, Brentford, Enfield, Illford, Dagenham, Croydon etc voted Labour and are by and large known as run down/working class (not Ealing itself but the borough in general)
White flight comes into account too, Ruislip for example is essentially a BTEC Essex. Thing is nowadays what used to be white flight areas are now as diverse as any area in London.