Because he can start a new company knowing everything that he got wrong the first time around, be able to hire absolute badass engineers who got fired from Nvidia because some Manager or HR thought they smelled wrong and was a hygiene risk, or quit Nvidia because they didn't like the work they were being assigned, be able to raise capital from investors who currently won't invest in Nvidia because of reasons, be able to strike new deals that hasn't happened because someone at Nvidia isn't letting them happen.

Nvidia is a very old company, not as old as Intel but close. Old companies build their own internal overhead you just cannot get rid of that would just kill a new company