Their own proofs contradict them. Flights on airplanes trying to debunk curvature show a sun of the same size as from the ground. If it was closer and smaller, it would seem bigger as you got closer to it. Its clearly very far. Same with how the moon follows you as you drive.
The sun and the moon are said to cycle overhead, which makes it impossible for both solar and lunar eclipses to be true. Even if one is closer, one 1 type of eclipse is possible without some forced mechanisms. Yet we see both in reality.
The space model fits all observations and perfectly predicts future events with zero contradictions. In my view, its not even close. It may seem fantastical due to the perceived truism of the concept of down, but logic can go down many paths, and only evidence free of preconceptions can point one to the only truth.