Verant has an in house utility for creating items. (yeesh, do I have to explain this?). When they create a new item, they have a lot of templates. So they take the "leather tunic" template, change the AC, weight and a few other things and then set the races to big, but they don't feel like removing the other classes from the item they are editing (since it doesn't really matter anyway)
Because it is leather and all those classes can wear leather. If they didn't leave those classes in the description and decide to one day expand the class choices of the large races then they would have to go into the item database and change every item that they would be able to use that they couldn't before. This way they don't worry about that.
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