My completely unresearched and speculative opinion as to why Disney prices are high and will stay high for the time being.
1. Scarcity of ships. Seriously, they only have four ships, compared to the dozens that each major cruise line has (NCL, RCL, Carnival, Princess etc, etc). So, supply and demand. Don't need to sell as many cabins to be fully loaded.
2. Load factor. Assuming (with conditions) that your marginal cost (cost of operating the ship vs amount you need to collect in fares to break even or profit) is very narrow. You are then highly dependent on pricing your cruises to get to near capacity or full each trip. Plus, you have the costs associated (more food, more cleaning and service staff), more water usage, more fuel use for electricity etc. Some costs are fixed regardless of how full the ship is, but others do vary. So, Disney in charging twice as much as other lines, but willing to operate at 75% full, probably still has higher profits then the fully loaded ship sold out at lower per person costs. (Granted, maybe Disney has slightly higher costs due to quality of staff, entertainment, but I doubt this is much of a factor).
3. Disney brand - there are some people who will only go on a
Disney cruise. Other lines don't have this advantage.
4. Co-branding with Adventures by Disney -- some of their European packages are combined with cruises, and these package vacations are also highly priced, so this also drives up the cruise price on some itineraries.
5. An easy way to get Disney Vacation Club members to expend their points -- and high cruise prices means they can get people to spend more of their points then they might on land hotel destinations.
6. Uninformed people who don't do their research. Just as people will sometimes pay too much for a car or a house or an appliance etc, there are enough people out there willing to pay Disney's prices. Unless they see a dropoff in their bookings, they are charging what the market will bear.
7. Disney willing to let cabins go empty at higher prices up until closer to cruise date, and then has an efficient sales and promotion strategy to top up the ship at lower prices for unused cabins but still at a profit.
8. Beverage sales and add ons make huge additional money for Disney (as well as other cruise lines).
So, could some of these factors change in the future?
1. Two additional ships means more cabins to fill. So, this might have a slight impact.
2. Competition from other cruise lines. They are priced lower and have more options. At some point, this could cut into Disney'd market share.
3. Cost of operating. At some point, if you don't have enough bookings, you are operating your ship at a loss. I think Disney will get to the point where they need to ensure they are closer to sold out to maintain their profit margin.
4. Overall global tourism competition or economic factors are unknowns. Could result in discounts for Europre destinations, but on the other hand, could drive up costs for Caribbean trips leaving from US ports being more popular
5. Seem to be growing complaints about quality of the Disney food and service. So, if demand goes down because of this, they have to reduce cost to bring demand back up to their profit load levels.
Overall, though, I think the factors keeping Disney's prices high are going to continue for a long time. It doesn't matter how much people complain or say they are taking their business elsewhere, there seem to be enough core returning cruisers, and a market of new ones, coming on board willing to pay Disney's prices. Until demand drops off at their current prices, they will stay at this level.
I'm not eligible for any other discounts.
Most people are "willing" to pay more because its literally the only price they'll ever see. Trust me, if playing the "wait and see if a privilege discount comes out for me" game would apply to me then my habits would change also, I assure you! 
