Little or no demand for bulk cargo carriers. Planes like the An-124 or A300-600ST are very specialized and do specialized jobs pretty well. Plus ocean shipping may well be better for bulk cargo ops intercontinentally. Plus the 747 is familiar... cheaper, readily available. And does FedEx need to life 200,000 lbs of bulk cargo from unprepared dirt strips in the middle of nowhere?
Stop drop and roll will not save you in hell. --- seen on a church marque in rural Virginia