If I'm reading your comment correctly, you've got it backwards. Most people (around 60% in 2017, down from 80% in the 2000s) believe in a JFK assassination conspiracy, and it's never been a majority believing that Oswald acted alone. So the question is: how is it that most people believe in a conspiracy, when the evidence overwhelmingly points towards Oswald's sole guilt?
The answer: by misdirection and lying about the evidence (compounded over decades). Oswald didn't shoot from a "great distance", it was 59 yards and 88 yards for each shot, whereas he had to shoot at distances of 200 to 500 yards when he qualified as a sharpshooter in the Marines.
https://news.gallup.com/poll/165893/majority-believe-jfk-kil...
How is it possible that the woman appears to be sawn in half?
How is it possible that most people believed jfk was shot by a lone gunman from great distance?
The same principles apply.