There's three reasons people tend to prefere Yag over Ai.
-Ai have all that boring trashmobs&barricade part which prevent people to make others runs after the first one.
-Ai's first boss, hard to lead, explain and succeed in a pug (i'm not even talking about the need of a decent geared & xp'd tanks)
- Ai looting only one epic leggings.
Maybe it would be more popular with 2x leggings guaranted drop.