The CMs who make PSes have no control over what is made available, nor do they have a stake in how early or late you plan to dine. If you are offered only early seatings, it is because there are genuinely no late seatings available. The restaurants do not close early if they don't have any late PSes, and the only time that you will be asked to dine early is if you are booking the Fantasmic package (which is a consideration for you so that you don't miss the show and you're not rushed through your meal.)
We want you to eat when you want to eat, and some times fill up faster than others. There is no advantage for the CMs involved to book seatings for any particular time.