The seven private British airports are run as a proprietary business which is sensitive to the needs of its customers. BAA has staff whose role is to survey airport users. These surveys enable BAA to determine who their customers are, where the service problems are, and maximize the quality of service.
An airport such as Metro which handles millions of passengers per year has many expectations placed on it by the people who use it. Different customers look for different things (restaurants, meeting spaces, ease of movement between gates) and an airport which lacks services will not be popular among the people using the facilities or the airlines serving those same customers.
Also, in a situation such as Metro where one airline dominates a large part of the airport and a specific terminal and set of concourses, the airport operator might wish to enter into a lease agreement for the whole terminal complex with that airline. At Metro, for example, the new owner might lease the terminal used exclusively by Northwest to Northwest who could then operate it or sublease the operations to a terminal manager. This would give the airline greater control over the facilities it uses and allow it to integrate all facilities for the benefit of its passengers.