I can imagine reasons why they wouldn't. It could potentially cause more issues with server performance since it has to account for more items. It could cause issues with items being balanced with other items that exist in the game. And the fact that it's really not that necessary. There's already a lot of options for different classes and builds, and for different types of equipment load outs for each class/build.
I'm not against more equipment in the game (as long as it's properly balanced with existing items, which is usually never the case when they introduce new items), I just don't see it being a priority, or one that will make me less involved in the game.
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