I remember hearing that when Universal was sold to NBC, the Lockheed site was not part of the deal, and Vivendi sold it.
I don't know if that is true, but I guess the reality is that maybe Universal realized that another park isn't needed and maybe never will be needed in already, theme park saturated, Orlando. Some could say that now yes it is not needed, but maybe 15 or 20 years yes, but wouldn't they still have to pay property taxes. Maybe they figured it isn't worth the money, since they have to pay taxes and also clean the property.
It would be screwed up if Universal sold the properity because they knew that the property would never be allowed to be used for residental or entertainment purposes, due to the site being polluted.