Why audiences are buying tickets to ‘Waitress’

Call it the Sara Bareilles effect. “Waitress” has played more than 700 performances on Broadway, after opening in the same season as “Hamilton,” which swept the 2016 Tony Awards. Part of its staying power has come through the show’s marketing efforts, which evolved to target what advertising company RPM sees as the driving force behind the musical — Sara Bareilles fans.  RPM launched the agency in August 2017, with the “Waitress” account in tow. At first, “Waitress” marketing leaned into the all-female creative team and the message of the play, with ads aimed at showing that the dark comedy had…