I will quote Anthony DeStefano's Mob Killer

"Peter 'Bud' Zuccaro, a Gambino crime family associate who testified against Charles Carneglia. Zuccaro aspired all his life to be a gangster but passed up the opportunity when the Mob wanted to initiate him into La Cosa Nostra"

He blames Gotti's flashiness and the changing face of La Cosa Nostra from secret society to being in the public eye as his reasoning.

From The New York Post

"After Gotti’s death, Zuccaro turned down the chance to become a made man after becoming disillusioned with the mob lifestyle.

He began drawing away from the Mafia and refused to take part in a hit on a Queens bagel shop owner who was suspected of having an affair with the wife of Gotti’s younger brother."