It has been. Dak is trying to take the next step as a QB, getting rid of the ball quicker.
If you'll remember, previous to this, Dak was more of the wait in the pocket type until someone broke open. He was a reactionary QB. It appears that they're trying to make him a proactionary QB, one who throws much more quickly before the receiver breaks open. Problem is, to do that you absolutely must have top notch field vision, you must know where the Ss and LBs are at all times. Dak doesn't have good field vision.
Why are they trying to change him? Because holding onto the ball as long as he was led to injuries and sacks.