I'm not even sure many/any of those ads in the link were in anything resembling a mainstream publication in the first place.
Does anyone know if there is a term for that kind of "bias" or self-deception?
The odd reflexive impact of that seems to be that today's historians and social sciences people are prone to falling prey to the "bias" and then weaving it into preconceived notions and narratives due to other biases like confirmation bias.
History never has much to do with what actually happened, anyhow.
You see it all the time on Facebook, or reddit, or wherever people post things like 'Did you know <group of ancient people believed> <something utterly ridiculous> without quantifying whether or not this was a common belief, or just a drinking story that they told.
An outsider who isn't careful about this might make a similar claim that modern Americans believe in a heroic lumberjack giant called Paul Bunyan, who has a giant pet blue ox. This is technically correct, but is also utterly useless as a description of modern Americans.
A more interesting phenomenon is where media consumed by a tiny group of well-educated wealthy elites is considered universal or common. There's no way the New Yorker had a bigger circulation than Hustler in the 80s.
edit: according to wikipedia, Hustler's peak circulation in the 80s was 3 million copies a month.
That's probably a consequence of those same elites controlling the media.