Who else operates to Lagos these days, from a major European airport?
Apart from the two carrying the union jack, you can get to Lagos from Europe with:
Air France - Paris CDG
KLM - Amsterdam
Iberia - Madrid
Lufthansa - Frankfurt
Turkish Airlines - Istanbul
NDB17 has got it quite right. Arik is definitely not trying to make a profit with its long haul flights. It's all about the prestige, which is probably why Mr. J. doesn't like to use LGW as it is clearly much less prestigious to fly to this second class airport. Same goes for the New York route where they use JFK with an average of 40 pax or so per flight...