I spent a lot of time trolling conspiracy forums as a teen, young adult.
Got to meet a lot of oddly held views. I did find the article I read interesting in that is said that people who agree with one conspiracy likely to agree with others, even if contradictory.
I was a teen in the 1970s, when there was a strong anti-government, conspiratorial "vibe" that I could sense, particularly in the post-Vietnam/Watergate period when there was widespread mistrust of government and its institutions. It just seemed to be the natural thing for citizens to question and criticize the government - along with questioning their motives and trying to come up with some plausible explanation for the things our government does, from 1776 to the present day. Everything had come under scrutiny and was being openly challenged, including stories of "how the west was won."
It was in that kind of atmosphere growing up that I heard a lot of conspiracy theories - although nothing about flat earth. Some were more related to strange theories without necessarily implying conspiracies, such as theories that aliens visited Earth at some point in the past, theories about the Bermuda Triangle (which I haven't heard about in years), the lost continent of Atlantis, Loch Ness Monster, Bigfoot, etc. These were strange beliefs, but they challenged the conventional wisdom at the time, so they may have gotten some attention for a while.