Cherry pick much? There was no internet, there were print ads and highly specialized subscription magazines (Starlog started in 1976, etc.), posters, short TV ads in B&W or color if you were lucky, radio, and one probably had to drive to the theater to see long trailers like that. Don't let the ease of embedding an archived video on YouTube today confuse you with the effort it actually took in the 60s to see trailers like that. Entertainment Tonight only started in 1981, then Siskel & Ebert in 1986, and you had to be willing to tune to PBS for that.
Let's see every official trailer - or lack thereof - of every movie released in the 1960s with the release dates of the trailers and movies, how often and where and what time they ran (TV, theater, other), how many people saw them compared to how many people saw the movie, how many people demanded the kind of detail available today, the print ads, photo releases, and number of reviews, the saturation of reviews and set photos and plot points relative to the general public, and how many films were seen only on the basis of the star (John Wayne, etc.) or the genre, perhaps with only a minimalist slogan or logo (e.g., Alien in 1978 - the egg with "In space no one can hear you scream") and nothing else.