2D doesn’t have foreground and background. If I change my perspective on a painting, I see no more nor less than what I saw before.
Slightly off topic but the best 3D movie I’ve seen is a documentary on the Hubble Telescope. Much of the prep work and space work was documented via 3D cameras. The Hubble itself can provide 3D visuals via its movement and the astronomers can very accurately use Hubble photography to take the observer flying into actual 3D star fields.
That DVD alone was worth my bucking up extra for a 3D television.
The amount the Hubble can move is far too small compared to the distance to any of the objects it looks at for this to be at all relevant. Even if you move clear from one side of the Earth’s orbit to the other, and even if you look at the nearest star to the Sun, the parallax will be less than an arc-second. For those fly-through starfields, scientists use a variety of other methods to measure, calculate, estimate, or outright guess their distances, and then construct a 3D model based on those distances that’s basically independent of the Hubble image.
How is this different to requiring a projector and screen? Are those films not true 2D?