I assume that for most of history, pubic hair was not trimmed or shaved in any way yet I often hear it being associated with the 1970s. Is there a reason for this?
OK, so I wasn't sure I could answer this to appropriate standards, but I did find a few things to cite, sort of, although admittedly much of this is nevertheless based on inference. Also, it goes without saying, any link here is probably going to be very NSFW. Click at your own risk.
I can't speak to the standards of pubic grooming throughout history, although I'm sure there are periods of time prior to the modern era where shaved or trimmed pubic hair was common, but I can say with a good deal of confidence that the reason we associate the 1970s and "full bush" is pornography.
Premiering in 1972, "Deep Throat" was "the first breakout hit from the then-niche market of hard-core pornography" ^[1] . Prior to that, smut had been relegated to the fringes, but "Deep Throat" opened on 300 screens nationwide, and was a major leap over the previos generation of adult-oriented films which had seen relatively wide release, such as "I Am Curious Yellow", in that it featured graphic, up-close penetration. ^[2] The floodgates, so to speak, were now open, and pornography was revolutionized, within only a few years being considered a billion-dollar industry, churning out full-length color features which at least pretended to have a plot. ^[3] . Productions such as the "Devil in Miss Jones" and "Behind the Green Door", quickly followed, the former, along with "Deep Throat" making the Top Ten list for profit of all films in 1973! Plenty of other films were released in the "porn chic" period, and sum of it is, there is a reason this era is called "The Golden Age of Porn" A number of other films gained some level of recognition, but I don't believe it is necessary to list them all. The point is that the '70s saw a mainstreaming of pornography, at least relative to its place in society previously, and, spearheaded by "Deep Throat", "sparked a cultural debate on pornography that continues to this day" ^[4] .
Now the fun part. This is Linda Lovelace's pubic region. Here is Marilyn Chambers. Georgia Plevin. Constance Money. Kay Parker. I could go on, but I think this illustrates the point. While you certainly can find examples to the contrary, the big names of '70s porn, and most of the productions, features "full", or at most lightly trimmed, pubic hair.
Now compare this to the stars of today, for which I will use the AVN Award for Female Performer to illustrate.
Almost all of them show either fully shaved, or a very trimmed appearance, certainly not approaching the level seen in the '70s. It has become the defacto standard, with plenty of evidence pointing to unshaved being relegated to essentially a niche or fetish ^[5] . My point isn't to dwell on this, as analyzing why this shift in preference has happened isn't really within the purview of the subreddit (try /r/AskSocialScience, maybe? Source [5] does discuss this a bit if you want to look into that factor, as does source [6], which I'm not directly citing, but did browse through and seems to be worth mentioning if you want to read up on why the shift has happened), but rather to illustrate the contrast. Porn is, I would venture, the main way that we see other people naked, and thus a major driving force of what we consider "normal". When we see the flicks from "back in the day", that was normal grooming then, but because it is so different from what we see now, it really stands out in comparison. As I illustrated at the beginning, the '70s was really the first time that really enters the popular conscious, so while people might have had the same pubic grooming standards for decades prior, it is the '70s that it really stands out in, since it was certainly gone by the '90s, if not the '80s as well (AVN Awards only go to 1993 though), leaving only that decade or so window for us to have a mass of pornographic media with "full" pubic hair.
[1] "Inside Deep Throat", Review by Tom Doherty, Cinéaste, Vol. 30, No. 3 (Summer 2005), pp. 61-63
[2] '"Somebody Somewhere Needs to Draw the Line': Deep Throat and the Regulation of Obscenity in Little Rock", by Timothy G. Nutt, The Arkansas Historical Quarterly, Vol. 69, No. 2 (Summer 2010), pp. 91-116
[3] Porno Power", by Dan Georgakas, Cinéaste, Vol. 6, No. 4 (1975), pp. 13-15
[4] "Dirty Little Secrets: Scholars, Archivists, and Dirty Movies", by Eric Schaefer, The Moving Image, Vol. 5, No. 2 (Fall 2005), pp. 79-105
[5] "Smooth talking: The phenomenon of pubic hair removal in women", by Leonore Riddell, Hannah Varto, and Zoë G. Hodgson, The Canadian Journal of Human Sexuality Volume 19 (3) (2010): 121-130
[6] "The Hairlessness Norm Extended: Reasons for and Predictors of Women's Body Hair Removal at Different Body Sites" by Marika Tiggemann and Suzanna Hodgson, Sex Roles (2008), 59:889-897
Edit: Tightening up sources a bit, and adding a bit on why things have shifted.
