Here is a little experiment you can do at home…

Take a ball, doesn’t matter what kind. Basket ball, beach ball, cue ball, doesn’t matter. On that ball, glue, tape, or otherwise attach an object, preferably something that sticks up from the surface, like a pencil. Then, while holding the ball in front of you with the attached object on top, rotate the ball away from you. You’ll see that the object disappears from view from the bottom up. Scale up, you have a globe and a ship on the horizon. This would not happen with a flat object, because the attached item or pencil or “ship” would have to go over the edge of the flat object, say a plate for example. Easy experiment you can do at home with any spherical object.