On 11 Aug 2013, I wrote up a `working definition' of Film Noir:
the world is darker than you think
There are implications in the word `darker' here.
Three unique things came to American popular culture, and through it to Hollywood commercial movies, in this time period:
Basically, Americans lost their innocence as they confronted questions such as basic identity (wife or welder? man or murderer? provider or provided-for?), saw their world and its assumptions turned on its head, and were asked to ponder ideas they never had before about motivation, morals, and mental `illness.'
So, film noir both soothed and aggravated these deep anxieties.
Film noir sprang from this loss of innocence. It cannot occur to a generation that was never innocent to begin with. The modern (post-1970) dark films, the neo-noirs, are more homage to past styles and tribute to and partial send-up of the attitudes that underlay the noir years of the 1940s and 1950s.
Adding to this is the whole subject of technology and style. Hollywood moved from black and white film stocks to color, and the film grains shrank and stock grew faster, capable of registering images in less and less light. All these technical changes made the rich, stark chiaroscuro possible to a 1946 black and white film very difficult, even out of the question to a 1963 color film. Though it might be possible in a digital age to recreate the characteristics of 1940 polychromatic black and white film, doing so would be merely an exercise in style, a deliberate affectation, rather than working with the tools available to explore the problems of the day.