A Common Cause
Societies need a common cause to usefully exist:
This creates a feeling of Ownership—and that is exactly what a functioning society needs.
It’s also about channeling the ambitions of your ambitious people. When there’s no proxy Status Game to play, they have to tackle the problems themselves. Nice.
Probably a big reason in itself not to create any kind of Bureaucracy.
For the US, this might have been domesticizing the Frontier/the Industrialization, but there have been other great tasks, too.