Why did John Travolta dress in drag for Hairspray instead of casting a pure female actress?

John Waters' original 1988 film comedy "Hairspray" starred Divine (actor Harris Glenn Milstead in drag) as Edna Turblad. When the film was translated into a Broadway musical in 2002, it continued the concept of having an actor in drag play Edna. In the original stage version, she was played by Harvey Fierstein, who won the 2003 Tony Award for Best Actor in a Musical.

The success of the stage production, which was nominated for 12 Tonys and won eight (including Best Musical), prompted a movie version of the musical. And so the tradition of an actor in drag continued with Travolta in the 2007 screen edition of "Hairspray."