Why not make the Blu-ray a 2D/3D combo Blu-ray?

[joenostalgia23]

The reason they have separate 2D and 3D discs is because, often, neither of the L/R eye will match the 2D version.

This is true of animated films, like Disney's Tangled, where the depth of field is different in the 2D version so just watching the Right eye of the 3D version wouldn't be the same.

The same is true for 3D conversions, usually both eyes are modified from the original 2D capture. And in some films like Jurassic Park, the 3D version is different in ways like adding additional atmospheric effects like rain into a shot.

There are movies already that have the 2D and 3D versions on the same disc like Dredd or Journey to the Center of the Earth. But it is more common when the film is actually shot with 3D cameras.

Finally, sometimes a 2D BD is desirable because it can maximize bitrate for the 2D only transfer. Or alternatively, all of the special features are included on the 2D disc so the 3D disc can only house the 3D content.