"The audience will not undergo anything the protagonist does not undergo. For the journey is the same, and the audience members understand themselves to be the protagonist—as, indeed, for the length of the evening they are, for the drama is their dream, put forward by their representative, the dramatist; and we know in our dreams each character stands for the dreamer."
So proclaims David Mamet in his book, Theater, and, on this occasion, I agree with the dogmatic/problematic writer/director. If our lead characters are not invested in their stories, by no means should you expect an audience to be invested. Of course, I'll take it one step further: if the author is not invested in the journey, neither will the lead character be.