I was referring to more recent years when conspiracies have appeared to multiply: Q, pizzagate, birthers, "rigged" elections (2004, 2012, 2016, 2020), Seal Team 6...(of course, Hofstadter's "Paranoid Style in American Politics" shows a much longer trend).
I don't know why it has occurred. As media has to compete more for viewers they also have to sensationalize stories or people will not watch. CNN started out as a hard news station with little politics. People will not read hard news and quit taking newspapers. They want simplicity and thrill that demonizes the other side all included in a Facebook meme.
I have read some interesting books about the cultural split that talks about group behavior and identification. It is from well established research, but I'm not sure why it is affecting politics today. It shows we will choose our group over another even when it is imaginary. One experiment divided people into 2 imaginary groups. They gave them the choice of giving everyone from both groups $100 or giving your group members $60 and the other $40. Most chose the 60-40 even though it meant your side got less.
I have friends and relatives who quit going to Wal-Mart because they heard they gave money to Biden, quit watching professional sports, quit watching certain actors or musicians because of their political views, won't buy Nike.....It just creates more hostility and spreads hate and eliminates things we previously enjoyed. And, I think it is contrary to free market capitalism which rewards good products for decent prices. And, liberals are the same way but their enemies are Hobby Lobby, Chick-Fil-A......