Without trying to excuse it, I wonder if there's an element of "we're beating Chelsea - what do we do now?". At least when it's 0-0 you can feel obliged as the home team to attack. Go a goal up and we haven't got the quality to defend a 1-0 lead, nor are we likely to continue to bomb forwards in search of a second.
And I know we went 3-0 up at Arsenal. I don't know how to explain that one.