^^ Mind demographics too. Europe has a very small population, with only several middle size countries.
France, Germany, Benelux and UK together have about 230 million inhabitants on an area of 460,000 square miles. This is one of the most densely populated areas of the earth. The distances between the four largest airports in this area (LHR, CDG, FRA, AMS) are in no case further than 400 miles, which is not a worthwhile distance for an aircraft. The well-developed road and rail network handles most of the traffic in this part of the world.