Why was Taft called the chief of justice?

I doubt that Taft thought much about being a Supreme Court Justice while he was

President. However, after he was denied a second term as President and forced to retire he needed something worthwhile to do, He was a long time legal scholar and no doubt in the past had a dream of being a justice and when the Republicans won the White House again he had his chance and Harding was happy to nominate hiim.