Why? IMHO, it is because we have lost our souls to political correctness run amok and empowerment of progressive goons. It is even hard to write a novel now adays that delves into the vagaries of the better angels in the human soul. Apparently there is too small a market for things not loaded with sex and degeneracy. I am a fan of the BBC mysteries, like Inspector Morse and Midsomer Murders. The newer offerings are degenerating as a reflection of different, more ‘tolerant’ writers. Even the Dr. Who series is overly influenced by the sexual preferences of the writers and directors who are ‘gay’.
Your point about the ever present agenda nowadays rather than the timeless theme is spot on. They, quite simply, don’t make them like that anymore. I doubt they’d have much of an audience now anyway.