I think there are two reasons many people don't get PCS.

First, every brain has different tolerances to injury. There are also many variables between the person and the forces of the impact. Add to this the possibility that many may not remember prior impacts or sub-concussive impacts and the likelihood of the PCS impact causing PCS from Multiple Impact Syndrome is increased. Just because one does not remember prior impacts does not mean that they did not happen. The very nature of concussion creates a situation where a remembrance of the impact is likely to not be remembered.

Second, It is suggested by anecdotal evidence that those with higher intelligence tend to demonstrate PCS symptoms more than those with lower intelligence levels. Many people have very low self-awareness skills or even skills of being aware of their surroundings. Those with higher intelligence tend to have a greater awareness of themselves and their surroundings. Then there is a mis-application of symptoms since many do not demonstrate PCS for days or weeks after the concussive event.

It takes strong hindsight to connect the concussive event to the myriad of symptoms, especially if there was no head ache at the time of the impact.