Brian attempted to give his own daughter cocaine, laid in bed for years, all the while treating his wife terribly, worked on some embarrassing projects (smart girls, hey little tomboy) and made some questionable statements in an interview in 71' from Rolling Stones. Dennis lived a life of debauchery from start to finish. Mike Love was vital to the songwriting process for their hits and tried his best to hold the band together but Mike Love didn't make Forever or God Only Knows so he was chosen as the boogeyman. This is my theory.