Yes, ego and "respectability" were part of Bonanno's motivation (the book was BS but it was interesting), But, I think another reason was to get back at the Commission:

The Commission deposed him as Don after Joe Colombo ratted out his and Magliocco's plot against Gambino and Lucchese. A long, destructive internal war ensued, and both Bonannos went underground. Joe resurfaced in 1966 but by that time few were left in his family who were loyal to him. So, he stepped down as Don (so he says, but I think the Commission forced him to recognize the obvious). They gave him a pass in return for his retirement.

The book has plenty of nasty stuff against other Dons. But, the most important thing is that Rudy Giuliani, who was then US Attorney for the Southern District of New York, read it and found in Bonanno's description of the Commission the perfect description of a Racketeer Influenced Corrupt Organization as defined by the RICO Act. It was the basis of his successful prosecution of the Dons in the famous Commission case.