It’s because stupid people elect them.
So if you’re in a line at the bank or something like that, and if the people with you in line are representative of this poll, then chances are that either the person in front of you or the person behind you doesn’t know that the Earth revolves around the Sun. And if you include the next person in line behind / in front of them in that group, chances are that one of them thinks the Earth has a hollow core, or that it’s frozen or some crazy shit like that.
In fact, usually you do have to wait in line when you go to vote. So think about that: people who go to vote to elect people to make incredibly important decisions which affect all of us (by that I mean humans and not just Americans) can’t even grasp the very basic reality of our situation here on Earth. 41% think astrology is scientific? That’s just barely more than the percentage of eligible voters who turned out to vote in 2010.