Too many coincidences beyond what is statistically probable compels the skeptic to question the orthodox narrative of an isolated incident theory. Ie: Nothing to see here, it was simply an act by a single person completely independent of the various persons he had contact with preceding the event.
So although it’s not impossible that Oswald could be a lone kook who for whatever reason felt compelled to shoot JFK, the amazing variety of persons that Oswald had contact with , characters like Jack Ruby and George DeMorenshield, or Guy Bannister, or in a photo with identifiable Alpha 66 BOP operatives, makes it extremely difficult to accept Oswald was just an isolated nut.