George Lucas may have spilled the beans:

In a Bloomberg Business Week story about Disney’s buyout of Lucasfilm, the Star Wars creator reveals that Lucasfilm “had already signed Mark and Carrie and Harrison — or we were pretty much in final stages of negotiation [when the Disney deal came about]. So I called them to say, ‘Look, this is what’s going on....Maybe I’m not supposed to say that. I think they want to announce that with some big whoop-de-do, but we were negotiating with them,--I won’t say whether the negotiations were successful or not.” 

More on the story here.