The massive jumbos were built to service the largest airports, when most long haul service operated on a "Hub and spoke" model. This is when the big international airports serve as a "hub" for the vast majority of incoming flights, where people would then connect on to another flight which would fly a shorter distance to the final destination. However airlines, for a number of reasons, have shifted more towards using smaller, more efficient aircraft that serve more direct routes. Larger aircraft also require bigger runways, which means they are not as flexible as smaller craft.