The Nofollow attribute indicates if the source of the link "trusts" the destination of it. Trust is a very critical element in human relations and not one of the easiest.
Too much mistrust can lead to paranoia and isolation. Too much trust can lead to abuse and being taken advantage of. We learn from childhood that you have to learn to trust, but also have a "healthy" amount of suspicion and mistrust if it is justified.
This is often not a very rational process, but driven by instinct and emotion. Most people experience in their life’s at least ones that their strong trust was a mistake, which in some severe cases result in complete mistrust and paranoia.