There is a lot of evidence that that model of the cosmos is true! Which also makes it plausible (though it does not prove) that people unaware of most of the contrary evidence would accept such a model.
- Rain falls from the sky, but water does not flow uphill. Therefore there must be a supply of water already in the sky. However, that water does not block our view of the sun, moon, and stars, so it must be farther away.
- We see lights in the sky, but if you try to put a light in the sky without something holding it up, it falls. Therefore there must be something, a structure or firmament, holding those lights up. Such a structure would also serve to hold the water, and so is consistent with the previous item.
- The sun, moon, and even (with careful observation) most of the stars, are seen to disappear below the horizon on one side of the world and reappear some hours later on the other. Therefore there must be an underground connection for those objects to move through. Water flows downward, so those underground spaces must be filled with water, which still allows passage because it's fluid.
- Most stone and earth, however, sink into water, so something must be holding the surface of the earth up. A solid structure underneath, like a pyramid, could do that but would block the passage of the sun and moon. Pillars, however, can hold things up while allowing things to pass underneath.
... and so forth. People back then weren't stupid; they just didn't know squat about how anything really works.
Respectfully,
Myriad
