The reason the sport has evolved is the reason Football or any sport evolves... people just get better, and they learn from the generation before them... That is way you saw Roy JOnes Jr. and FLoyd mayweather Jr. do things that had never been done in the ring, or Tyson for that matter... Defensive techniques, feints, and the like are always evolving as boxing becomes more of a sport, and less of a form of battle.