Why so many people believe in the flat earth?

Basically, the reason is because it's written on the bible, Genesis.
https://imgur.com/ZvkOz7s

Not only that. It's written in the OLD TESTAMENT.
https://imgur.com/oRpbbDc

So, since you can't disconnect Christ from Genesis, since he mentions Adam and Eve in the new testament, people connect one thing to another, by reading the bible. There are more than 3 billion people in the world today that are from religions that use or are derived from the Old Testament.

You don't understand why they don't believe in science, because you were exposed to an environment of learning and not exposed to a religious environment like the people who believe in Flat Earth were.

Our mind can play tricks on us, there are counter-intuitive things. I'll extend this post whenever I can!