It would probably not require much effort on the part of the dev team, since the 'Loot All' button in the UI is already there (top left corner of the Loot window), some people are good at taking only what they need from the world, but some can be hoarders (and who is to blame them, it's the apocalypse, right?)   This would also go a long way to help prevent real life injuries such carpal tunnel syndrome because the player wouldn't have to micromanage the mouse so much while on looting