One thing that is strikingly apparent in photo 38 of President-elect John F. Kennedy seen surrounded by a huge group of mobbing Harvard students: in the photo, there are only TWO cameras clearly visible. One is a twin-lens reflex, and the other is an 8mm movie camera. AMong this huge group of students, and there are TWO visible cameras...and the same goes for the huge mass of British protestors at an anti-nuclear protest shown in photo #3, in which we see what appear to be two working press photos, one with a three-lens turret equipped cine camera, and the other with a 35mm camera, both stationed in the lower left corner of the frame...I also see a guy carrying a trumpet...
In today's world, at both of those types of events, we would expect to see literally HUNDREDS of cameras and or cell phones with cameras. The lack of cameras in the hands of the general population 50 years ago might explain why "iconic photographs" exist from so many mass events. Fewer photographers, fewer photos, and the photos that do exist were often shot by those working for official outlets, with the capability to distribute the images world-wide (UPI, AP, etc).