Sometimes that is certainly part of it. Do you go out of your way to explain calculus or particle physics to children?

Or do you simply not bother?

When a person has spent their entire life trying to communicate whatever they were excited about to people who are only interested in the fad du jour, they don't develop the skills to communicate well once they do find people bright enough to understand.

For example, go walk around MIT, Harvey Mudd, or Cal Poly and see how poorly freshmen do with their initial social gatherings.

You personally are probably extremely smart (this is HN after all, where I seek refuge from the total fucking paste eaters of the world) - but that just means that you were dealing with someone who had never had an opportunity to learn those communication skills. Unlike you, presumably.