I'm sure it's mostly heat and prices.
Slightly different topic but it has to do to heat and exhaustion, one thing i never understood about Disney is why not put some creative effort into easing the burden of waiting in lines. Like have long benches throughout the entire line so people can sit and just scoot down as the line moves. When people are hot and tired the last thing they want to do is wait in a 45 minute line while standing the entire time.
Also they need more places to sit throughout the parks that has shade. I know its not aesthetically pleasing but i feel they can put more areas for people to sit and rest. Heck put them underground or something.