I am not exactly sure why they moved it back, but I think the main reason is staff and schooling. and possibly campers and school. Like with me, the whole thing of getting out on the 12th and then camp starting on the 15th would be craxy. Most of the schools in the state have similar schedules, and a lot of our staff come from local-ish schools.
"I'm always pretty happy when I'm at camp with you!"