A lot of the Apollo work also got done in basically one administration (Johnson largely continued JFK’s policies). As soon as Nixon was in charge, NASA got gutted, and then they only had the resources for shuttle. Later Apollo missions got cancelled because Nixon thought the money was better spent killing more Vietnamese people.

Switching administrations means vastly changing policies, if for no other reason than the new boss hates the old boss. SLS “succeeded” (got hardware made and launched, at least) where Constellation failed partly because they buttered everyone’s bread in the right way.

HLS is dumb. SLS is dumb. But similarly to Commercial Cargo and Crew, it survived administration changes partly because NASA wasn’t directly at the helm, so the new guys didn’t just hit the big red stop button.