Why do people even now still believe in a flat Earth?

It's funny, I was doing a project on the history of astronomy and I needed to find some medieval beliefs about astronomy and one of them was of the flat earth. So I googled it and I found that there is something called the flat earth society and that they even have arguments that "prove" that the Earth is flat. I just found it extremely amusing in that they applied extremely faulty logic, such as the moon being round and therefore unable to hold an atmosphere and ocean but somehow able to keep all the dust on it from falling off, and conveniently ignored all the evidence, such as photographic evidence, that proves the Earth is round. I mean I can understand if they were very religious why they may believe that the Earth is flat and 6,000 years old but this was not a religious argument and they were trying to use pseudoscience to actually prove their point. I just can't fathom why a non-religious and presumably rational person could possibly believe that the Earth is flat.