FIVE REASONS WHY THE SHOTGUN FELL OUT OF FAVOR
I think the shotgun fell out of favor for a number of reasons
1). The competition-centric focus on scores on a target. It is easier for a range officer to score a rifle target than a shotgun pattern. Killing is not a concern when scoring is the concern.
2). The increase of frail people in the public and private sectors tasked with using weapons. A 5'0" 110 pound kid can be shown marksmanship with an AR, but a 12 ga may be too much. It is not an all-inclusive, egalitarian weapon.
3). Did I mention that people seem to be weaker and softer these days?
4). The unwarranted fear of needing to account for every single projectile. Even with an SMG or Pistol, that is impossible and I submit that due to its nature, there will be fewer misses with a shotgun.
5). There are no Daniel Defense or Noveskes in the shotgun world to market them, and few full-sleeved, neckbeards on Youtube champion them...and as we know with the new generations...looking cool is almost more important than being effective.