It's not hard to find 30% of any given population that's monumentally dumb or ignorant about something. Consider, for instance, that the median IQ is supposed to be about 100. This means half of the population has an IQ below that.
When you look at things in the aggregate, it makes sense.
It's also not unusual for many people to lack knowledge that isn't relevant to their daily lives--like the rotational period of Venus. Most of us here like
learning and gathering knowledge. But it should come as no surprise that a great many people don't. Many of them are too busy just trying to survive to worry about collecting what is ultimately (to them) trivia.