Shotguns have terrible risk/reward in PVE. PVE has penalties for death ranging from annoying to extreme. The most likely place to die is close range. Bosses typically one shot you, majors and ultras don't go down fast enough and will kill you at close range. Finally weak mobs tend to come in packs and can most easily kill you at close range. To top all this off we get mobs with perks such as light switch or angry or elemental burn. Even with the shotgun buff it may be a nerf if range is further reduced. In PVE you just can't close range and reliably stay alive. If you die you face an extreme penalty.