Why can't any completed item be upgraded by Ornn?

Also, because it would be a lot of work to go through and make another ugrade for every single item and since ornn can't choose which one gets upgraded anyway it would be even more work and pointless And because having all of then would mean every time any item got changed ornn would also have to get changed instead of just 8 specific items

Because there is a limit to how many items he can upgrade per game and I would rather not have to do a bunch of maths to decide what item to upgrade and what not to upgrade. Most builds in the game already have an item Orn can upgrade. It's literally a waste of time to allow every single item in the game to be upgradable since it will very quickly devolve into "only upgrade this group of items the rest are trash" and have people flame you for upgrading the wrong item

Because not every item is important enough to Ornn to demand his time upgrading.

He only likes the best of the best.

Not to mention that 90% of builds have an item ornn can upgrade anyway