The Interesting Part of the Moses Story

The story of Moses has long been the stuff of legend, but why did they exclude what could arguably be described as one of the most interesting parts of the Moses story? They just totally left it out of the film. The interesting part is the part that we don't see displayed on the stage or big screen. At no place in this story are we told why God would send Moses on a mission of rescue and then suddenly decide to punch his ticket.