I would be more willing to ruthlessly prune my vault if there weren't so many nerfs or buffs of weapons or perks that will render some gear useless while making other types good. Like Subsistence on weapons - not a great perk before this season because it dramatically reduced your ammo count for that weapon. But now the penalty is gone and the perk is a lot more useful. This is why people hoard things. It really sucks when you find out the mediocre weapon you deleted is now this season's God roll. As for armor, transmog has been good in that people can now delete mediocre armor they were just keeping for how it looked. But for Exotic armor there needs to be a way to reroll for better stats. I keep multiple copies of my Exotics so I can fine tune builds for each season. Once you play the game for a long time with three Guardians you end up with a lot of Exotics. In summary people do need to prune their vault to a certain extent but the motivation and need to keep extra stuff because of how Bungie is always changing the rules of the game is real.