What's behind the depressing, naturalistic "grime" tone of 1970s movies compared to those before and after?

This will sound familiar to anyone who has seen a lot of films, but it's something that has always puzzled me: Movies before the 1970s had a lot of theatrical polish and tended to fit into certain fixed boxes, and movies after the 1970s had a different kind of theatrical polish and fit into a new set of boxes, but '70s movies were relatively free-form, lyrical - even messy.

It's not exact, of course - some late '60s movies moved in the direction of this style, and some early '80s movies were still part of it, but it was a definite phenomenon. Actors in these movies looked disheveled, un-made-up, natural - they looked like people on the street. Places where people were shown to live looked thrown-together instead of like color-coordinated sets, often with natural lighting, pretty much like how real people live.

These movies showed small, gloomy apartments and shabby houses rather than wish-fulfillment homes. They were grim even when they were light-hearted, carried an atmosphere of weight and realism, and were much less likely to disappear up their own asses into fantasy.

Some example films: "The French Connection" (1971), "The Friends of Eddie Coyle" (1973), "Serpico" (1973), "Mean Streets" (1973), "Dog Day Afternoon" (1975), "Rocky" (1976), "The Deer Hunter" (1978), "The Warriors" (1979), etc. It wasn't monolithic - there were plenty of movies that showed the seeds of future formulas: "Patton," "Enter the Dragon," "Star Wars," "Animal House," etc. But the influence of the "grime" trend was clear even in those proto-'80s movies, in choices of styles and somewhat pessimistic viewpoints.

A glib interpretation would just ascribe it to the cultural influence of the Vietnam War, urban decay, and disillusionment with American society. But I'm not aware of any similar movement in Depression-era filmmaking, when people would seem to have had a much more immediate sense of social and economic failure. So why would 1970s audiences wallow in gloomy themes and depictions if previous (and future) generations sought escapism?

Let's consider crime films, since that's where it seems starkest. In 1960s crime movies, criminals are relatively clever, organized, well-dressed, and act out predefined roles to suit the plot. They drive fancy cars, they live well, and they have beautiful women.

If that sounds familiar it's because it's the theme of every era after the 1970s too: The slick gangster entertaining the audience with his witticisms and choreographed action. Even savagely gritty movies like "Robocop" (1987) used criminals as agents of shallow entertainment rather than literal characters.

But compare that with "Dirty Harry" (1971), which was a '70s version of the action cop genre - the criminals are not entertainingly evil, they're slimey, sickening garbage that practically leave snail-trails across the screen. It's more realistic than other eras, even though it's trying not to be, and that's normal for the period.

Violent crooks are shown realistically in movies like "Serpico" and "The Friends of Eddie Coyle": Lazy, sleazy, cruel, ugly, predatory liars, with no theatrical embellishments to make you like them more. They live in crummy apartments, and their actions have nasty consequences that are portrayed coldly instead of hammed up with melodrama.

The same is true of any kind of villain: The studio executives in "Network" (1976), the spies in "Marathon Man" (1976), even supernatural evil like in "The Exorcist" (1973) - they're shown with dispassionate disdain.

But then at some point in the '80s movies start being more interested in having fun than showing you something weighty. The decade is covered in some of the most vapid (and fun) movies ever. The grime is just gone, and in its place is a neon-colored adolescent dream world set to a driving soundtrack. What the hell happened?

Then with the '90s, even with the return of supposedly serious movies, they're still not nearly as serious as the '70s - they get very stylized and choreographed, and squeezed for emotional effect. They're operatic instead of jazzy. And it's never really gone back.

Even with later films that were distinctively "gritty," they were very simplified and sharply-cut, usually lacking the kind of naturalism and depressing gravity of the 1970s films they consciously imitate.

Perhaps the best explanation is the most cynical: Substance is an art rather than a product, and Hollywood ever since the 1980s has been all about mass-production rather than quality. Only a rare and vanishing breed of auteurs has the resources anymore to deliver quality movies entirely their own way without letting studio script-surgeons maul it with formulaic rewrites.

It's so rare now that totally honest, realistic movies about the lives we see all around us look foreign and strange. Actors who look like people rather than computer-generated faces with perfect symmetry seem radically out of place on a big screen.

So, we can guess why the 1970s era of realism went away, but it's still sort of mysterious why it came about in the first place.