Disney blacks out more APs when they expect the largest tourist crowds. This is their way of trying to bring the crowd levels down so they don't exceed park capacity. More tourists, especially those outside SoCal, equals more demand for hotels. That in turn increases the cost per night for a room. So if you are looking at August when many kids are on summer break and families can travel, then the price is higher is higher. There are still many schools who don't start their school year until just before or right after Labor Day.
Also the hotel stay for some (not all) are less then the tourists. Since I have to fly, I need a hotel the night before we go to the parks and the night of our last day in the parks. Depending on where they are coming from and how often they visit, many tourists will add day trips to Universal Studios, LA tors and San Diego while using their DLR hotel as a home bases. All of this increases demand and drives up the price.
I hope this explains why AP blackout dates, especially when schools are out, doesn't equal lower hotel prices.