It's because electromagnetism has a chirality or "handedness". Check out Maxwell's On Physical Lines of Force. On wiki page 53 he says this: "A motion of translation along an axis cannot produce a rotation about that axis unless it meets with some special mechanism, like that of a screw. This is why we have dynamos and electric motors. You push current up the wire and the motor turns, and vice versa. Note Maxwell's mention of "vortices" in his title. You can emulate electromagnetic attraction and repulsion with opposite and similar vortices. Two opposite vortices move together, two similar vortices move apart. Gravity isn't like electromagnetism in that it doesn't have a chirality. It's usually depicted via the bowling-ball-on-the-rubber-sheet analogy. The problem with this is that it uses gravity to "explain" gravity, so remove the bowling ball. Your rubber sheet is flat. Now emulate an electron by grabbing the rubber sheet with your left hand and twisting it anticlockwise. Emulate a proton by grabbing the rubber sheet with your right hand and twisting it clockwise. Now take a look at the sheet. It's a bit screwed up where your "hydrogen atom" hands are, but away from your hands, there's no twisting because the two opposite twists cancel. However there is still a resulting tension. This reduces with distance, altering the motion of waves traversing the rubber sheet, causing them to veer a little towards your hands. That's like light bending when it passes the sun. You have emulated a gravitational field. For matter falling down, you need to know about the wave nature of matter. See if you can work it out.