What's the point of limiting the availability of special items to a timeframe, then once the players who have it eventually stop playing the game, and those things are lost forever? Literally never seen or enjoyed. Ever. The END.
Every anniversary, you can stock the crown store with items no longer available, and make them high cost.
Happy players, happy developers and artists. Rewarding, fun, festive, promotional -- Win Win Win.
As an artist and binge collector of artistic items, I am appalled at the idea that the ACTUAL successes of ESO's art team can, and will often become extinct.
I understand ZOS was attempting to keep the items more rare, so that their "uniqueness" stays intact, and obviously, well done. However you can bring items back here and there and still maintain that aspect. By limiting it to once a year and making them more expensive, you keep these items in the game and preserve their rare and unique appeal.
Don't look into someone's eyes, if you fear what they'll see in yours.