https://www.polygon.com/fortnite/2018/9/11/17845634/fortnite-drum-gun-vaulted

Fortnite’s drum gun has been vaulted after months of in-game dominance. The change comes as part of patch v5.40’s content update, which is already live.

While the Fortnite team at Epic didn’t give specific reasons for its decision to vault the drum gun, the reasoning seems clear. When the popular meta began to shift away from shotguns and toward SMGs late in Season 4, the drum gun became the game’s standout weapon.