From Seth D. Baum, Jacob D. Haqq-Misra, and Shawn D. Domagal-Goldman:
...A third response to the Fermi paradox suggests that ETI are actually already widespread throughout the galaxy but are somehow invisible to us. The ETI could be unintentionally invisible, if it just happens to take some form that is undetectable to or otherwise undetected by humans. Alternatively, the ETI could be intentionally invisible. The intentional form of this solution is sometimes known as the Zoo Hypothesis  because it implies that ETI are treating Earth like a wildlife preserve to be observed but not fully incorporated into the Galactic Club...
Preserve? Or resource?
In any event, there is a potential explanation why we never got to the Tomorrowland of the Kennedy era. You just don't let the big predators loose in the neighborhood. You keep them behind the moat.