The recent deregulation worldwide has sparked a huge increase in the # of low-cost airlines, resulting in a spreading out of passenger load across airlines. Therefore, there aren't as many passengers to carry per airline as before, and A380s and even B747s are no longer needed. In fact, all of the U.S. airlines (Delta, United, American, and smaller ones) are either phasing out or parked all of their jumbos.
Side effect:
Because of the # of increase, air traffic has worsened (e.g. delays at airports) and pollution has increased very rapidly.