Having seen the access fees for several airline's lounges, both home hub and out-station, there's definitely good 'cost recovery' money to be made when an airline has the main lounge or the only lounge in an airport, as well as when it has a lounge that's so much better than the alternatives – LHR being a very good example of this.

(Yet, the fact that anybody goes to the BA LHR T3 lounges at all is also proof of how few people know about Oneworld reciprocal lounge access based either on class of travel or status, so I enjoy taking the opportunity to educate people on that score at every chance.)