Airports have to work with the airlines to try and meet their needs, otherwsie there is always the option for them to take their business elsewhere.
Low cost airlines (Ryanair) can be very demanding for the airport authority because they demand ever increasing standards to help them achieve short turnarounds, on time performance and cost effectiveness. Airlines such as these may demand simplified processes / facilities to reduce their costs but these come at a cost to the airport as their facilities are usually designed for a diverse type of airline traffic (unless of course you look at the ex-military airports which offer simple processes and negotiating the terminal is quick and uncomplicated). Often the airport will offer 'competative' landing fees and airport charges to attract these airlines. The benefit for the airport is attracting an airline which can rapidly grow the airport's passenger numbers which increases revenue through things such as car parking and retail spend. These reduced fees however do mean that the airport may not be in a financially robust position to invest in the types of facilities the airlines demand at no additional cost.
On the other hand you have full service airlines such as BA which have their different challenges. Working relationships can often be more productive as these airlines are willing to invest. i.e.
investment in T5.
Airlines don't always consider the consequences of their actions on the airport and consequently their own service. i.e. airline implements new policy which the airport is not consulted on,can not therefore faciliate so it impacts on other aspects of the operation - finally impacting on the service offered to the airline's customers. Great ideas not thought through?