A lot of work goes into making models. Sometimes, only for them to be seen one time, in the background.

In order to solve the problem of them only being seen once despite all of the work that went into them, game developers find clever ways to re-use them. This is so entirely logical that a lot of games do it. They re-color enemies often to the point you'd never guess they are recolors; they re-use old bosses as regular mobs and sometimes they are so small and recolored that you don't notice it; they get enemy models and make small adjustments (such as removing horns or adjusting wings) before recoloring so it seems like a different model and of course, they re-use armor.

There are so many things they have re-used that I actually took many, many years to even notice it. Often they are just good at doing this, while other times it's obvious.

Armor specifically doesn't bother me. Especially if it's consistent which is a new set and which is a re-used set ie. I just glam over crafted gear.