If you're playing with someone who steals your loot, they don't understand the game.
Or you dont understand what competitive questing means.
Hmmmm... Nope, my answer is right.
It's called Competitive
Questing. For the most part the game is still co-operative and players still need to co-operate to progress. There are still fights against always-hostile enemies, and fights tend to be difficult for solo players to win, so depriving a party member of important equipment is just going to make it more difficult for the other party members to contribute to the common fights and common goals.
Hmm. Lets say there is a goal which could be achieved by me or you. Meanwhile we will face some other enemyes, yes. But, if I hid some equipment for you then I reduce your chance to get the goal. It means, "smarter" or "social" thinking player says - We should proceed.
But individualist says I am going to win. Nothing else matters.
There are two main types in theory of games.
Game with zero sum result - typicaly RPG cooperative party game
Game with non zero sum - like poker
When you install competition to the zero sum game then you have changed the very base. The new rule is here, As the Highlander says " There can be the only one."