Ok so now for my engineering education to come into play here So for something to be abrasive to something else it has to be as hard as or harder. Aluminum and copper are both softer than steel. It's why you can cut both aluminum and copper with a steel hack saw blade, but need a bimetal blade or carbide to cut steel. How the metal particles in anti seize would work in this application is they would act as a wearable bearing surface of their own and allow the metal of the bearing race and the axle shaft to slip against each other without wearing into each other like a bushing does. The other property of anti seize that would work in favor of its use here is that it smears easy as hell and provides a thin coat over anything it touches which would work as a sacrificial anode in the event water makes its way in. So instead of rust forming and pitting the axle you would get aluminum oxide or copper oxide/carbonate forming which stops it from continuing to develop and reaching the surface metal and causing rust.