The U.S. boxing scene, from a participation standpoint, has been steadily declining from it's peak (1920's-WWII) for decades. For a variety of reasons, foreign competition wasn't in a place to exploit it like they are now. Economic growth and better career opportunities took away far more boxers than rival sports- as migrant ethnic groups moved up the socioeconomic ladder, their need to box was eliminated.
People who like to watch the Klitschko brothers and most of the other top heavyweights have to be gluttons for punishment. Give me the smaller fighters any day! In addition to being far more skilled, they have a far greater work-rate and much more heart. - Chuck Johnston