Its one of those small ongoing frustrations. You win something (like the current Winter Veil Disguise Kit) which, being a repeat reward of many years, many of us have had drop multiple times - and we can’t just vendor it to our handy mammoth mount vendor. Because, why? Yes, its a toy. Even if it was made vendorable, it would require a deliberate act to dispose of it. Put a warning on it if you must but for the love of small hairy goblins, just let me click sell and see it woosh away. Instead of having to drag it out, type DELETE and click on it.
Thank you and Merry Winter Veil.