As others have said, it's how the industry work giving different prices for different seasons and different prices for different features. Every hotel has three general seasons Peak, Shoulder and Low. Prices are reduced in low season to entice guests, increased in shoulder to keep a profitable rate but still somewhat enticing, and raised to full price in peak season when no enticement is needed.
Charging more for an upscale room is influenced by the cost of running the room, the furnishings of an upscale room generally cost more to buy. Better quality of everything from carpets to chairs to mattresses etc. And they cost more to replace and generally have to be more frequently to maintain the upscale value. That's built into the pricing.
And, amount of inventory and demand come into costing. There are only so many desirable rooms in a hotel ie closest to lobby/restaurant etc and the demand for those few rooms is high. Higher pricing is one way of controlling demand on the premium rooms. Besides, it's well known in the industry that people don't believe they've recieved a premium room unless it costs more.
Bottom line, Disney is doing nothing that all of us in the industry do.