Gravity is particles, moving, just as magnetic fields are, and there is a polarization in gravity, which we have explained as the repulsion force. Before mankind discovered that magnetism was polarized, they discovered it as an attractive force. Metallic items stuck to the sides of magnetized rock - how curious. After centuries of digging about in this phenomena, humans have satisfied their curiosity to the extent that they understand that magnetism is a force field, has a flow out from one pole and in at the other pole, that the Sun and some other planets are magnetized and line up with each other. They still don't understand the cause of this force field, or its nature. Magnetism is caused by a particle, in motion, as we have explained. What other explanation is there for a force that reaches out and affects another? Magic?
The bi-polar aspect of magnetism is only apparent when what occurs in nature can be countered in the laboratory. You force magnetized objects to do what they do not want to do - touch north pole to north pole or vice versa. Then you can observe the bi-polar nature. In gravity, you are seeing but one aspect in the positioning of the planets, and dealing with a phenomena that does not lend itself to easy experimentation. However, experimentation is possible, in space and away from the surface of the planet. The repulsion force fills the gap in some of your other theories where you have no explanation for discrepancies.
In magnetism, the simple flow of particles creates more than a force for alignment, it creates an attraction. The gap is filled. Like water in a stream, where flotsam eventually lines up in the center, evenly spaced, just so magnetized objects do not keep their distance when free to move. They approach each other, and attach like a string of pearls. Likewise the phenomena of gravity, where the desire to fill the gap causes objects to approach one another. It is only where this gap is overfilled, by the presence of two large objects coming near, that the repulsion force is expressed. There is no room for the flow of gravity particles, so the objects stay apart!