In continuing the above, going into the 1970s, aliens were the new gods. All the old mysticism gave way to a new sort of scientific mysticism. But for all the same reasons. One was a lack of the individual imagination of a person to think people could do something, or something could happen without some sort of super intervention or super power. In that past, it was super-natural, in the present it became super science. People hold perceptions of reality to their own limitations of knowledge. "I couldn't build the pyramids. I can't think how other people could build the pyramids. Something else must have". Another is this sad plea of hope to a cold, uncaring universe for someone to care. Aliens visiting us meant we had space friends and could feel warm and safe in that knowledge. Which oddly gets distorted to the other end of there also being evil aliens who want to get us, which satiates our instinctual need for hate and fear and grows out of our human instinct towards paranoia that what we felt was good (alien friends) is fleeting. Preparing for the bad feeling by making it happen by inventing the idea of bad aliens. And visiting aliens are both made up anyway.
If you feel that means your fellow humans are emotionally primitive, wrap themselves up in knots of their own invented phobias and happiness and psychosis, and that because of their flaws the humans race can never fix the human race, then you may fall into that camp of people who are looking to the stars for someone to save you because only an outside intelligence could then make that change. And we've tied ourselves into an interesting knot there.
That's a very thoughtful consideration of underlying motivations.
I boil it down into a poster:
Scientific Literacy doesn't stop the human imagination and human bias. To give an extreme example, the very high level of PhDs amongst members of the Aum Shinrikyo death cult (most famous for the Sarin attacks in the Tokyo Underground) who have since openly admitted much of their interest and later fanaticism was driven by interpretations of Asimov's Foundation Series and various anime shows like Yamato. Both blatantly have no grounding in reality yet a lot of people with science related doctorates very much enjoy sci-fi so they embraced it - particularly they embraced the image of the Foundation's role in Asimov's galaxy, where eggheads save civilisation from itself.
Wish fulfilment is not the case here (well not nessecarily) but you get the idea - being better educated doesn't stop humans giving odd ideas a chance if they are intrigued by them. The great Emperor explains above why the Ancient Astronaut Theory particularly appealed to people at the time.
Ancient Astronaut Theory is very interesting as a concept. I read Chariots of the Gods as someone who knew the gist and had no confidence in the idea. Purely because its a neat idea. On release I can see more 'normal' people in your more scientific world ultimately throwing it in the trash but probably wouldn't effect initial sales or the people who embrace it as an idea as opposed to a realistic theory.
Compared to other UFO-related groundless pulp science coming out at the time its also a lot more sober then books that talk about Reptilians and Plaedians living underground fighting transdimensional wars against the Nordics all the while the US Air Force is retro-fitting tech from the Greys, generations -even eons- ahead of ourselves but not bothering to use it, etc, etc.
EDIT: Sorry, in relation to the OP maybe he can't find a semi reputable publisher and it ends up just one of many of the 'nutter' books like I alluded to above with a hideous cover and it gets lost in the shuffle. Maybe poor sales see him beef up the wierdness to appeal to this UFO hardcore and it remains very much a minority interest book "Martians Built the Pyramids with Android Slaves!".
This limits relatively mainstream 'historical' ufology to interpretting supposed pre-Roswell saucer sightings while Ancient Astronauts in its much more garish form is considered really weird. Bit like the divide between general members of the public and the more hardcore set on the matter of MIBs. To most its a series of high concept comedy films and they are simply government agents. But UFO enthusiasts know the truth - they know they are robotic servitors of an Alien race.