> people never hold their cameras upside down

I'm not to sure about that. I rarely keep my camera (close to) fully horizontal.

Also for macrophotography when you want to have the camera very close to the ground on a tripod, upside down is often used.

You don't have to. There are GPS satellites along the horizon too. As long as it isn't literally upside down.

Turning your camera upside down is an old trick to see over crowds, since the viewfinder is now at the bottom.

This trick is also used extensively in submarines.