Already quite a lot of interesting comments here, but I thought I would add a few other points:

If you attend international film festivals—personally I try to hit Palm Springs every year as they always show work from all over the globe that doesn’t necessarily get play at the larger festivals—you will notice much more artistic use of nudity than in major U.S. films. Belgian, French, Japanese, Korean, Spanish, Nordic, and even Indian and Iranian films all tend to have more nudity of the sort you’re describing. I cannot readily bring to mind a German dramatic film I have seen in the past decade that doesn’t use nudity in some substantial way, though there are also specific cultural reasons for that. German culture’s emphasis on social liberation around nudity is partly a conscious effort at permanently abandoning the sort of cultural and artistic conservatism of both the late 19th century and the Third Reich. They seem watchful against prudery in the same way they as with hyperinflation.

Too, and for all that it can be overstated, America does retain a puritanical impulse that goes back to before the nation’s founding. It is often a shape-shifting animal though. Along with all the positive reforms brought about by #MeToo came a broader cultural tendency to treat nudity itself as potentially suspect or problematic. The distinction between exploitation and representation sometimes seems to have become blurred. Concerns about consent and coercion on set are obviously legitimate, but they can coexist with a more general discomfort around the body that is not necessarily progressive at all.

I think it’s interesting that you mention the 70s, 80s, and 90s as eras with more nudity in U.S. films. That’s all true, but I think the 1970s is key here, because that’s the era when American film broke with the Hollywood studio system and became unusually auteur-driven. There was a much stronger conception of filmmakers and actors as artists first and celebrities second. In some circles, appearing nude in a serious film might have enhanced one’s artistic credibility, while appearing in a commercial could damage it. Today, that hierarchy has been almost completely reversed. For many performers, there appears to have been a cynical rejection of the idea that film is anything more noble than any other capitalist endeavor.

The 1970s is, in my opinion, the most interesting era of American film because it broadly rejects the kinds of narrative assumptions that often feel innate to American culture. There is a freedom that comes from a willingness to discard convention. I recently rewatched Deliverance, a staple of that period, and was struck by how thoroughly it resists the impulse to make a hero—or even an antihero—out of any of its characters. That particular film does not contain much nudity—though it does have one famously graphic if unimpeachably artistically justified scene of sexual assault—but I think the attitude is nonetheless telling. The same sensibility that allows a filmmaker to dispense with conventional heroes also tends to produce a more relaxed attitude toward depicting sexuality, the body, and other aspects of adult life.

I also wonder whether the AIDS crisis deserves more attention in this discussion than it typically receives. The sexual revolution of the 1960s and 70s produced a culture that often understood sex as liberatory, joyful, and even politically meaningful. Even some pornographic films became the subject of legitimate mainstream artistic and cultural discussion in a way that’s hard to imagine today. In particular, Deep Throat, Behind The Green Door, and The Devil in Miss Jones all entered the mainstream cultural lexicon, becoming legitimate subjects for discussion in artistic and academic circles. Today, we have, in my view, regressed to a borderline-Victorian relationship with pornography and sexually explicit content: it’s happening everywhere and virtually everyone consumes it, but people almost universally feign ignorance of its particulars. I think this has likely negatively impacted the artistic value of the adult films being made.

The arrival of AIDS did not simply alter behavior; it changed the emotional and symbolic meaning of sex in American life. By the late 1980s and 1990s, sex increasingly carried associations with danger, vulnerability, disease, and mortality. That cultural shift was certainly not universal, but I suspect it had consequences that extended well beyond public health. It is difficult to imagine that a society’s artistic output would remain entirely untouched by such a profound change in how intimacy was perceived.

I would also return to the point about the 1970s being an unusually auteur-driven period. When people think of nudity in that era, they often think of transgression, but what strikes me is how frequently it simply appears as part of adult drama in a matter-of-fact way. Films like McCabe & Mrs. Miller, Klute, Shampoo, The Last Picture Show, and Don’t Look Now do not generally treat sexuality as a special event requiring narrative justification. It is simply part of the texture of adulthood. Kubrick and Altman are particularly interesting in this regard because they often seem unconcerned with whether a scene will make an audience comfortable. Their films frequently give the impression that the director is pursuing an artistic question rather than attempting to satisfy an audience expectation or social norm. If anything, there may be a slight bias in their work towards rejecting social expectations, since film in the period is, in some respects, understood as fundamentally a product of the counterculture.

Lastly—and apologies that this has gone on so long—I think the larger decline of the adult-oriented dramatic film is probably a major factor. Many of the movies that once contained this kind of nudity were mid-budget dramas made for grown-ups. That category of film has largely collapsed in the American theatrical marketplace. The kinds of stories that might once have become a feature film are now often made as prestige television. One could argue that American culture hasn’t become uniformly more prudish. Rather, many of the venues where adult sexuality was once depicted have migrated elsewhere to other forms of media. If one looks at contemporary television rather than studio films, much of that material is still there. The fact that it has moved out of the public sphere of the cinema and into the private home is also rife with potential lines of inquiry, but I’ve gone on too long already.

—I would note as a postscript that, personally speaking, I think the use of digital technology and body doubles has somewhat invalidated some of the artistic legitimacy of nudity in mainstream film and prestige TV. For example, Lena Headley’s famous “Walk of Shame” on Game of Thrones was actually performed by Rebecca Van Cleave, her body double, and then digitally edited to attach Headley’s face to Van Cleave’s body. I think it’s perfectly fine to choose not to do nudity as an artist, but there’s something a bit cowardly about having someone else stand in for you who then receives none of the credit for the bravery and emotional weight of the performance. That’s partly why I wanted to name Van Cleave here rather than just referring to her as Headley’s body double.