/ic/ - Artwork/Critique

Why is the viewing height/eye height always the same height as the horizon line?

I'm trying to intuit it but I can't for some reason. I know even in space it wouls still be the same height, so it's some property of just where the eye is in relation to the subjects. When tilted down or up, horizon line will be same but with 3 point perspective VP added. Kinda makes sense in space but why is it always always the same on Earth no matter how high up you fly? I guess because it's something about the angle you're looking at. Like it's relative so looking straight "ahead" will always mean looking directly at the horizon, even if you're really high up. So the eye tilt will track downwards with the Earth's horizon as you go up. Oh and I also realized the horizon is really just a flat ground plane from the camera. So it actually wouldn't necessarily be accurate for objects way far below on a different ground plane you if you're high up in the atmosphere.