Because it offers a lot of passenger transport aircraft. If a serious accident or delay inevitably affect the reputation of the airline, which is the oil company's customers.
As a service to aircraft on passenger numbers. If a serious accident or a delay would affect the reputation of the airline, which is a customer of the oil companies.
Because it is available on many passenger transport aircraft If a serious accident or delay will affect the reputation of the airline, which is an oil company's customers.