When clay target games were making shooters shoot without a pre-mounted gun a short barrels was much easier for many to mount and handle a fast, shorter barrel. When they allowed the shooter to mount the gun then it became more about sightplane and follow through than mounting and swing. The 25" and 26" guns will be back in favor only when the game favors them and neither Skeet or Sporting Clays does that now. With modern powders and wads any barrel can be made to be about as effective as any other barrels legenth. So it comes down more to style of shooting than any other reason for the longer is better barrel usage.