The issue is called “survivorship bias”. The image you are looking at are from WW2 bomber planes that got damaged during missions but still made it home in one piece. The red dots are damage from enemy fire. The engineering task was to identify structural weak points and make the planes more resistant to enemy fire.

However the data on plane damage is grossly incomplete, because only those planes that survived are included in the data set. Those planes that took critical damage exploded and are not available for examination.

With that in mind, look at the diagram again. Those areas that do not have any reported damage are the actual structural weak points of the planes.