Everyone wants to stick to the plan of running the show continuously without any interuptions or repeats. But if they started now (eight episodes are already in the can) the season finale would air over the summer, when TV viewership is low. If they start in the fall, they'll have to take a break for the World Series.
They could start the season in November. But then it would probably end in March. They probably want the finale in May for sweeps.