I think the issue isn't that the Don is "not well known." The important thing is that the Don maintains a low public profile. Everyone knew that Carlo Gambino was the biggest Mafia boss in the country, starting with the fact that his family was named after him. But he maintained a very low public profile--he lived in a modest home in Brooklyn, never went "out on the town," never talked on phones or in places that could be bugged, never threw money around lavishly. One of the results was that he was never convicted of any crime while he was Don, and died peacefully in his bed.
Contrast Gambino's modest behavior to that of Joe Columbo (appeared on national TV, hosted rallies in New York's Columbus Circle); and John Gotti (the biggest loudmouth and celebrity gangster since Capone). Then consider how Columbo and Gotti spent their last years.