Huh, I hadn't realized it was account-level-only, but that makes sense, since I've never seen it on the post-a-work page.

What really puzzles me is what was the reasoning for adding it in the first place. It's not anywhere on the AO3 'Site Changes' blog so I think it's been there since 2009, when Twitter/Tumblr type propagation was way less prominent. Why was that considered a vital customization option way back then?