I think they are considering this deal for two reasons. These are simply my opinions based on observations.
First, and foremost, the theme parks in the Orlando area have already reached a saturation level. With 7 main theme parks to pick, most families on a week trip will never do them all and as a result are picking and choosing. I think both Universal and Disney saw this happen immediately after both IOA and AK opened. Instead of bringing hordes of additional people to either resort, the exisiting park's attendance were just "siphoned" away to the new parks. Disney hasn't really seen the overall resort increase they expected, the parks just spread out the attendance. Same goes for Universal, last year's attendance for the entire resort was a mere 3-4 million more than when it was just Universal Studios at its peak. That really wasn't worth building an entire billion dollar new park and expansion. As a result, for either Disney or Universal to build another park would be like suicide for their exisiting parks.
Second, and probably less a factor, may be the whole Universal sale to NBC. In order to make the theme park division look like a worthy investment to NBC, which have publicly stated they are considering selling off the theme parks to a separate company unrelated to Universal Studios, UO and USH need to show some major $$$. What better way for UO to make easy $$ then to sell off prime real estate.
Even if locals prefer Universal, that doesn't help the bottom line too much at UO since the driving force behind tourism in Orlando is "traveling tourists" and there are hardly any people who make a once-in-a-lifetime trip to Orlando and not visit Disney. But there are quite a few who stay on Disney property and never leave. UO has had nearly 5 years to prove themselves as a main drawing power to tourists, and even with, what I thought were, effective national campaigns (well, at least eastern coast campaigns) and numerous "free" offers tied to sponsering companies, Disney is still the far and away champ. For instance, MK alone attracted more people than the entire UO resort attracted. Its tough to compete against an established power house, even if you've got the goods.