Because NPC kings need to look good in shiny loot to give you a reason to attack them, not worry about stats.

My knowledge of things has faded a bit, but the first clue is the item limit.

I am assuming this is a limited item and it has zero stats beyond the armor one? I have seen more than a few limited items that were fairly terrible and would never be worn by any character.

Maybe it is highly valuable, so it is a useful selling or barter item?

You also just have to keep in mind some items are more for flare than anything else. You never know though. Maybe it is a secret part of a religious path and if you get a certain tattoo, and invoke it on the armor, BOOM super secret elite effects.

I know of one such item in the game that works this way, but only those in a certain religion would ever know it did something. Sadly, I never figured out where the item was before my char died.

There are also some items that are part of lich quests and the like which really don't have much other use.

Best to just move on from this one.