There's the story of David Cassidy. He got cast in the Partridge Family (the rock band family) largely because of his looks and his mother (Shirley Jones). His voice was set to be dubbed for the songs, but it turned out he had a golden throat. (The rest of the cast, besides Jones, could neither play nor sing.)

The producers hired top shelf songwriters to write the songs, and several hit albums were produced. (It really is good music, despite being bubblegum.)

Cassidy, however, decided that he had songwriting talent and chafed. He eventually left the show, and with the megabucks he earned on the show, produced albums. They're terrible.

The same thing happened to the Monkees.