I'm wondering how do Chief Justices of the United States get replaced? According to wikipedia, the last Chief Justice, Judge William Rehnquist was initially an Associate Justice. President Reagan nominated him to replace the retiring Chief Justice at the time, Judge Warren Burger.
When Judge Rehnquist passed away in 2005, Bush nominated someone outside of the Supreme Court, Judge John Roberts to become Chief Justice. I'm wondering, why someone on the current Supreme Court (at that time) wasn't nominated to become Chief Justice and an outsider was nominated? I would have assumed someone from the current Supreme Court (at that time) would have been nominated to become the new Chief Justice like Judge Rehnquist was and then nominate someone else to become the 9th Justice on the court.