Because he's just too slow to react and rather weak.
Walcott too, this blackburn side simply gave him space, otherwise he'll be a headless chicken. He's afraid of any contact, I think he should play table tennis only
Gerygooner that isn't altogether true. I think it is Arteta's return from injury and Song's return to form that made the midfield much stronger, not necessarily Ramsey's absence. Remember that the guy is what, 21? He is a very good midfielder for his age. Personally I think Ramsey would be better as a box-to-box midfielder rather than playing in the creative attacking role