I think you are close when you propose that other people who have had an experience like this are not willing to share because society stigmatizes them so that in the end, only those who knew them at the time or those who have become trusted friends ever hear the story.
This is certainly true for the people that I know. With the exception of the fellow student who felt compelled to tell his story, almost every one of the others that I know avoids talking about it and will even try to deflect conversation if there is anyone who hasn't already heard about it present.
One old friend still regularly communicates with me as I am one of the only people they trust to be non-judgemental since I knew them a long time before they had their experience. I get photos, short videos, descriptions of events, attempts to tie their experiences in with other reports, etc and so I dutifully check it all out to try to help them come to terms with what has become for them a lifelong process of dealing with an emotional trauma that ended up stigmatizing them back in the small town where we grew up. Long-term friendships are critical for helping people manage some of these experiences.
Events like this are relatively rare and so it is easy for someone who doesn't personally know or who has never personally had an unusual event happen to automatically default to the conclusion that the one reporting the event has some mental issue, is unreliable, etc. Another poster suggested that somehow the subjects of one thing I mentioned must have been confused by clouds. People look for the most likely explanations and tend to ignore the fact that many of these observers have more than enough experience to understand when they are seeing something remarkable. I can say that I know several people who have had strange things happen in their lives and that among that group there is not a single one who actively went out looking for that to happen. All were just ordinary people and some were still in grade school. I am open-minded about what has happened to these people and in some cases I saw the immediate changes in their personality and demeanor. Something different happened to them. I am not qualified to say what it was but I know it was not something that anyone would consider normal. I'm just trying to be a friend to them - a sounding board when they find themselves thinking about it again.