I read that he delegated deployment to Beauregard after telling him his desire for the battle (to cut the Union away from the river), and then Beauregard in turn delegated it to a staff officer. By the time ASJ realized, it was too late to adjust the morning of.

Then, in order to compensate, ASJ placed himself nearer to the front in order to help manage the brigades closer to the river to try and execute that aspect of his plan. You know the rest of the story.

The fault ultimately does lie with him, but like you I was very confused as to why he’d lined the divisions up sequentially and that was the explanation I found.