I talked to my mother just yesterday as they were getting ready to head home from the Polynesian and I asked her the very same question.
She said the weather for the last few days was very hot (around 92) with no afternoon rain to cool things off. Animal Kingdom wasn't too bad but the Magic Kingdom was packed. The Haunted Mansion had a 35 minute wait and It's A Small World had about a 40 minute wait. They didn't do much in the Magic Kingdom this trip.
Hope this helps.