I think you have to consider the context ca. 1950-1975. No Internet. No VCRs at home. Sure, there were stag films, but not so easy to obtain. You couldn’t go to the corner video store to get one. Obtaining them was not respectable even if it was your minister who did it. It was in a plain brown wrapper or under the counter.
And to play a movie you needed a projector. Very few people had 16mm projectors and they weren’t easy to rent or use for the average joe. So you went to the expense and trouble and slightly risque behavior only for bachelor parties.
So films with words like “fuck” were not common. The only openly-sexual films shown in theaters were Art Films like I am Curious Yellow, which forced you to sit thru long swedish political shit so you could pretend to be interested and get to the good stuff. And the good stuff was pretty tame to get past what censorship did exist at the time.
Then society, aided by SCOTUS, began to liberalize. Pussycat theaters were everywhere in Los Angeles; garishly lighted, unashamed, and beckoning. You took a girlfriend there and it became a little less sleazy than before to talk about and see sex even if the guy in the next row was breathing too heavily (I watched Deep Throat with a GF in a SRO theater).
Give the trend a few years, VCRs becoming common, and the Pussycat theaters went out of business. Not because nobody cared about sex anymore, but all could readily obtain tapes and watch them privately, something they probably wanted to do in the first place. Now they could. The Internet made it even easier – you didn’t have to worry that your minister would see you ducking into the X-section of the local video store, and he didn’t have to worry that you would see him, either.
Was oral sex not around in the 1950’s? Sure it was, but not as accepted, not as common, not talked about as much, not in the open. Did prudes exist? Sure, but they they had the upper hand and could control much of what we saw. Now, we can ignore them and wank, suck or fuck to our heart’s content in the privacy of our homes.
To go to another extreme, I have a small collection of sex and sex-related books from the last 100 years. One marriage manual from ca. 1910 mentions “the genital kiss” as being OK between husband and wife (only!), but has absolutely no information as to how it might be done, leaving it entirely up to the reader’s imagination. Yet this book proudly proclaimed, in the introduction, that it was shockingly liberal and should not be censored just because it talked about forbidden topics (like sex between husband and wife). I have no doubt that the authors (an M.D. husband & wife, of course) were really worried that they might suffer from Comstockery, rampant at the time.