They are a commercial company who will operate where it is profitable to do so - currently that is London for their cost structure and strong position in Heathrow, which has huge demand for slots and not enough supply. With resources tight, they are focused on where they make most money, which is not for them being able to base an aircraft away from the main operating base unfortunately.
They have no obligation whatsoever to serve any market in the UK; government's overruling commercial markets are much a think of the past - with any luck open skies with the US will remove all such tinkering.