I agree with your explanation but I think it's important to add one more imperative factor. You touched on it when you mentioned GM. In phase 1 Epcot had big corporations that sponsored every attraction. The corporate sponsors included AT&T, Exxon, United Technologies, Kodak, GM, Met Life, Kraft, Smuckers, T. Rowe Price, Coke, Nestle, IBM, Sperry Univac, GE and Liberty Mutual to name a few off the top of my head.
In phase 2 those sponsorships were starting to dry up. It was becoming difficult for all of the Disney parks to attract big sponsors as easy as they once did. Disney has a history going back to Walt's time to let sponsors foot the bill for construction and upkeep of many attractions. Those days are coming to an end and we're moving to phase 3.
Without sponsors to pay for the construction and ongoing upkeep of attractions, that cuts into margins. Therefore, as Disney stops being paid to sing the praises of corporate sponsors, Disney will instead sing its own tune and sell its IP. They've got to keep both Mickey and Minnie supported in the style to which they are accustomed.