There are a number of items in the game that are rare. Some of those are rare by design, eg. aetheric cipher. Others are seemingly rare through an error (like the Khajit Brazier, Enchanted praxis). And then there are items that, while not common, don't sound like they should be all that elusive, but you just never get one.
For me an example of that last category are dwarven construct repair parts. I have never once had one drop for me, despite multiple hours spent in dwarven ruins chasing precursor parts, ebon wolf leads, and the like. If I hadn't seen them in guild stores, I wouldn't have believed they exist.
How about you?
Ummm... you realize the item drops weekly from a very specific trial, some players may not even ever play that trial, so it's rare because you've never completed that veteran trial before (Halls of Fabrication)