Surely most airports are like that, apart from Heathrow to some extent, who due to the nature of the beast lose relatively few. Take another well performing airport, Amsterdam. A glance back to a few days spent there in 2005 - gone now are Lithuanian, Fly Air, Malev, Sky Europe, Ethiopian, Air Canada, Armavia, Air Moldova, Iranair, Pulkovo, JAL, Smartwings, Macedonian to name but a few. The skyline at Gatwick is dramatically different to 15 years ago, etc etc.
Don't forget that as well as economic and political changes influencing the changing nature of services to particular cities, immigrant/emigrant demographics also plays a part. The number of people heading to/from Canada in the 70s/80s was packed with people visiting relatives. As the generations move on, and those ties are loosened that number falls away.