They would have to dedicate server memory to track everything you have or have ever had in your inventory.
Think of all the weapons and other gear you pick up everytime you play and then dismantle it for materials. Now multiply that by the millions of people online each day. Now multiply that by whatever time period this info would be stored (a week? 2 weeks?) This would be a huge chunk of data eating up valuable server space.
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It would only be exotic weapons. Nobody really cares about anything else.