I think it's a case of simply being the least known Maiden song they're playing. Sign and Clan have been around alot longer and I think many of the less hardcore fans eventually discovered those songs from Rock in Rio videos and such. (Talking about USA, here)The weird thing is, for me, Greater Good has similar enough dynamics to Sign, Fear, or Clan that it's weird it doesn't get the crowd going. It's got its soft parts, heavy parts, fast parts, melodic parts, etc. To me it's just another 7+ minute great song in the setlist.