Why can't disney charge whatever amount they want to? If people will continue to pay at the current prices, then there is no reason to lower them.
I recently was driving on the New York State Thruway in the middle of nowhere, and stopped at a rest area that had a McDonalds. This McDonalds charged $10.99 for a #1 Big Mac meal deal. In my home town in NY, the McDonalds charges $5.99 for a $1 Big Mac meal deal. This McDonalds, like WDW, knows that if I am hungry, I am going to pay whatever price is needed to get this food, since there is no other option for me. If I had planned ahead and brought food with me, I wouldn't need to pay the extra price for the food. I was willing to pay for the convenience.
Also, when walking around in NYC, take notice to the price of umbrellas on rainy days compared to sunny days.
Like someone posted before, I think pre-paid dining plans, and especially the free dining offers have caused the prices to go up. The advertisements for dining plans state that you can save 20% by purchasing the dining plan, which probably means they jacked up the prices of the snacks and other food to offset.
I always get the dining plan (usually as a freebie, but will pay if no free dining is available), and therefore never pay for snacks, so I really have no idea how much any snacks cost, since they are "free". I also go to buffet lunches and make sure to get extra cookies, apples, oranges and bananas for snacks later in the day. Can fill up your "free" refillable mug at resorts with soda/water and bring them into the park. We bring plastic bowls and cereal from home, buy milk and OJ and eat cereal in room for breakfast for 1/5th of the cost of WDW breakfast.