why did mass effect 2 only sell 2.3m on 360?

[Pho_Hybrid]

Like everyone has said no multiplayer= no hit, it maybe the best of the year on 360, but when you have Gears2, 2 CODs RDR and Halo Reach all with multi and sand its not really going do so well, BTW do games like this do well on 360, RPG with no multi or sand box