We know there is an electromagnetic field; we don't know there is a spacetime. The electromagnetic field is a mathematical representation of the forces present on a charged particle at a point in space. The reality that creates those forces are electromagnetic waves which are very real. Spacetime is a mathematical construct; the reality behind it is matter waves. It is the waves that are being bent, not some imaginary spacetime.
Edited by Voltaire30, : No reason given.