To be able to travel outside the United States and re-enter more easily. A citizen enjoys the travel privileges that a U.S. Passport makes possible To be able to live outside of the U.S. and not lose your citizenship. To be able to run for public office. U.S. citizens never have to renew their certificates of naturalization. To protect yourself from changes that target non-citizens.
Government policy is based on whether individuals are citizens or non-citizens.