The main reasons they get caught are greed and stupidity--factors that trip up all lawbreakers, Mafia or not. Decades ago, when there was more discipline, the Dons were able to keep greed (mostly) in check, which reduced the risk of stupidity. Today it's no longer Cosa Nostra, it's Cosa Mia.

Joe Massino used to have his social club swept for FBI bugs. He found one, and actually returned it to the FBI who planted it. Later he was smart enough to close his social club, and to decree that all members of his family do likewise--the better to prevent surveillance.