What is the importance of the Free Cities in the novel, The Girl Who Drank the Moon?

The Free Cities lie on the other side of the forest from the Protectorate. No one from the Protectorate has ever visited them, but Xan travels there every year. The Free Cities know that Xan is a Witch. This is a good thing for them because Xan visits and helps them with health problems. Xan also provides the Free Cities with a baby to adopt each year, which turns into a holiday they call Star Children Day. The town celebrates Xan's arrival and she is treated like a guest of honor. Antain trades with people who live in the Free Cities because they want him to build special cradles for babies called Star Children.