In your heart you know it's flat
is the motto of The Flat Earth Society
On a gut level, it's much easier to believe the Earth is flat than to believe the globe theory. The shape of a globe is too hard to imagine - there are many confusing things about it, Mercator Projection, Great Circle Paths, latitude and longitude, magnetic north versus The north pole, etc. It's a lot easier for people to believe in the Flat earth theory, or else think of ways to make imagining it easier, such as Dyson Spheres, Ringworld, or the Hollow Earth.
People like their mental representations to be simple - that's why flat earth is appealing. Most people's everyday representation of the earth is flat, although they will apply the sphere theory when on working at a scale where it matters.