Walt Disney World has a reputation of being a family friendly place to visit, following Walt's philosophy of having a place where kids and adults can enjoy everything together. This is one of the things that makes Disney such a unique place to visit. But to many people (outsiders?), Disney World is considered a destination for kids - a place that adults tolerate simply to take their kids for a "once in a lifetime" trip so that they can say they did it.
Whether that status is justified is beyond the scope of this post, as is the stigma surrounding "Disney adults" (a topic I've considered discussing in more detail at some point). But on the surface, this is how Disney is seen to many people, and a place like Universal is there to appeal to people who "outgrow" Disney.