Oh, I know very well why. To the "progressive"-oriented TV networks and the "creative" community of TV producers, writers, etc. such orthodox characters are classified as "fundagelicals" and "bigots". If cast on TV at all, they could only be cast as villains.
What really needed to be said was countercultural in the 1960's and it is even more countercultural now. Of course, what needed saying then bears little to no relationship to what needs saying now, but I rest assured that NBC, et al, wouldn't say what needs saying until long after it is not worth talking about.
In Christ,
Deacon Paul+