Why was Tyagi not given an extension as SEBI chief?

Madhabi Puri Buch has just taken over as the chairperson of SEBI replacing Ashok Tyagi. Madhabi gets a tenure of 3 years and is the first woman chief of SEBI. Tyagi was originally appointed for a term of 3 years but was later given an extension of up to 5 years. So he has already been given an extension. He was to get another extension but the appointment committee has taken a decision of appointing the new chief.