Because he's told them: "The 7 per cent threshold is a staging post. When we get there we have to evaluate what has happened to productivity, what are the broader labour market indicators."
On the one hand the Bank is saying it will take 3 years to get down to 7%. On the other, City econimiosts are saying the threshold might be reached in just a year or two.
But the MPC does have to move as soon as the threshold is reached. Carney has reiterated that 7% is the point at which the " MPC will consider tightening".