"Disney bought Marvel Comics in 2009 for $4 billion. But years before, Marvel had sold the theme park rights to its characters to Universal Studios. Two years before Disney bought Marvel, Universal opted not to renew those theme park rights for the western half of the United States, and the Marvel characters left Universal Studios Hollywood in at the end of 2007.
Universal retained the rights for the eastern United States, where it had built Marvel Super Hero Island in its Islands of Adventure theme park in Orlando, as well as for Japan, where Universal's Japanese development partner had built a clone of IOA's Amazing Adventures of Spider-Man ride in Osaka's Universal Studios Japan. (I've not found any public documents that reveal what Universal is paying Disney, or paid Marvel, for these rights.) The theme park rights for Japan are under a long-term deal, said to last into the 2020s, while the Orlando rights are in perpetuity, meaning that Disney never will be able to secure the rights to use its Marvel characters in Walt Disney World's theme parks until it can convince Universal to give up those rights.
And in the business world, "convince" means to write a very large check or to fork over other capital assets that Universal would want more than to continue to be able to run Marvel Super Hero Island.
Disney has the rights to bring Marvel characters to Disneyland, Hong Kong Disneyland and Disneyland Paris (or to any other company's theme parks outside the eastern US or Japan), but it can't do anything with those characters inside theme parks in the eastern US or Japan. That's why the Walt Disney World monorail wraps promoting Marvel movies had to stay on the Magic Kingdom line. The Epcot monorail line goes into that park, so if a Marvel character were depicted on those trains, Disney would be in breach of contract with Universal, and liable in what could be a nasty, expensive lawsuit."
-Robert Niles, Theme Park Insider