Conversation so far:
who picks chief justice of the supreme court
The Chief Justice is appointed by the President and confirmed by the Senate.
who is the current chief justice of the united states
The current chief justice of the United States is John Roberts.
how long does the chief justice of the united states serve
The chief justice of the United States serves until they resign, retire, are impeached and convicted, or die.

Question: why
Self-contained rewrite: why does the chief justice of the united states serve a life term