I can see the point of that, but it gets a little more complicated when there's a disagreement between a minister and the Comptroller General, who is an official. Then the minister is ultimately accountable for what happens, including things having to do with rolling money into another fiscal year. But if a minister directs, it may be that it has to happen.
The formula in the Accountability Act is another way of dealing with it, wherein if there were a disagreement between the minister and the Comptroller General, the ministers of the Treasury Board would have to decide it.