Here's the big deal with LHR:
1) Hundreds of different connection to all over the world.
2) LHR is the premier UK airport and indeed a world gateway
3) Under 1 hour into the city (Heathrow express) Easy access by car, coach, bus etc etc.
4) Big problem for Gatwick is it's "charter airport" image, as all the major UK charter airlines fly from LGW. Business travellers prefer LHR.
5) Most important of all, flights from LHR to North America generally have high yield premium paying pax all year round, loads are likely to be higher at LHR than LGW on the same route if operated at LGW. This is why the likes of CO, DL, NW ,US are desperate for slots at LHR because flights to EWR, DTW, PHL/PIT, IAH, MSP, ATL are gonna have higher loads than LGW, and therefore make money.
In Arsene we trust!!