To be fair, I wasn't really there in the 70s. I mean, I was, but I was an infant, a toddler, I wasn't making movie-watching decisions just yet... Well, not really. But, I certainly didn't know why certain movies were the ones making money at the time. My experience with all of these movies so far this month came later mostly. Get to the 80s and I was plenty aware then (and in retrospect as well) why things were the way they were in popular cinema.
But, I'm not above speculation, obviously. Plus, I am capable of research. For example, disaster films were big--the Airport series, The Poseidon Adventure, Earthquake, The Towering Inferno, Meteor. James Bond films were in full swing with Connery and Moore. Crime was big--The French Connection, Dirty Harry, The Godfather and its Part II, Death Wish, Serpico, plus the wilderness movies, of course. JT Esterkamp at Medium, says "The films [of the 1970s] would be a reflection of the anti-hero as a protagonist. Watergate and Vietnam would be the two biggest influences on the 70's mentality. Film would keep the innovations of the 60's but abandon the youthful optimism that flowed through it." Weirdly, with something like the opening of Adventures of the Wilderness Family or Snowball Express, you've got a twisted version of optimism that arises out of cynicism. It's not youthful optimism, it's some sort of fed up, mature optimism birthed out of a world that stopped being optimistic. These family films can't help but separate their protagonists from the larger world because the larger world is where you get darker subject matter like The Godfather or A Clockwork Orange. New Hollywood, as it's called, was playing with the darker side of life, celebrating it. These family-friendly wilderness films were, at once, harkening back to something more innocent and relying on plot and character details that were integral to New Hollywood films. The antihero, the scoundrel, the pirate. And, sure they celebrate nature and getting away from "society" but they also rely heavily on the strength of familial connections and, when there's an antagonist at all, doing what is right. While there are men who try to kill Zachariah Coop at the opening of Across the Great Divide, the real story here is a struggle with nature itself, not unlike Adventures of the Wilderness Family. In New Hollywood film, the protagonist could be a bad guy. In those more family-friendly films, the story structure forewent the protagonist/antagonist setup altogether.
Meanwhile, you've got little ol' me, just learning how the world works, getting dragged to church regularly, and the moral structure of film was no longer black and white. Like my wonder at other people my age not being raised on movies yesterday, I've also got to wonder about people my age not turning into a bunch of bleeding heart liberals who wanted to know the villain's backstory because it was surely tragic. Hell, the original Star Wars trilogy was this writ large on the screen (and the followup trilogy it's inevitable overthinking), taking its cue from mythology in its antagonist being the father of the hero, but take that in context of US politics from the 60s into the 70s, the era of Vietnam, young men being sent off to a losing war because of what? Because of politicians, because of the Greatest Generation, because of their fathers. The best villain these wilderness movies can get is a bear, a cougar, wolves. If you're not actually going out into the wilderness to live, these things are just as much fantasy as Darth Vader is... Maybe more, actually, because anyone can relate to rebelling against their own father.