It's because they weren't spectators, and their only purpose in being there was to lure Jack Ruby. It was an incoming ramp, so who did they expect to turn in?
Q. Jack, when you left the Western Union office what made you walk toward the jail house?
A. Because when I drove by I saw some people down at the ramp and the curiosity had aroused me because of the flash in my mind seeing the people there because before I went to Western Union as I drove by on Main Street.
Ruby's going to the police garage was not his own doing, and it certainly was not something that the plotters left to chance. Undoubtedly, he was followed from his apartment to Dealey Plaza and then to Main Street. And they very likely had someone there at the ramp to coax him to go down the ramp. He never said why he went down there, and that's because he didn't know why he went down there. His mind wasn't even on Oswald as he walked down the ramp, and he had no expectation of seeing him. So, we're supposed to believe that he just snapped upon seeing Oswald? But note that he never reported that he saw Oswald.
Q. Did you know when Oswald was going to be moved, Jack?
A. I'll be honest with you, no.
Q. You had no idea?
A. Later on I found out he was supposed to be moved at 10:00.
Q. You were never told by anybody he was going to be moved?