Why An earth ground rod's job is to give lightning energy a short, low-impedance path into the soil instead of through your station or house wiring. Bonding the tower, entry panel, coax shields and the AC service ground to the same electrode keeps everything at the same potential during a strike, which is what prevents damaging voltage differences. Earth connections do very little for RF at HF and above, because even a few feet of wire is a significant fraction of a wavelength and presents substantial inductive reactance.
Watch out The idea that it reduces RF current between equipment is tempting, but equipment-to-equipment RF is controlled by short, wide bonding straps between chassis, not by a rod driven into the dirt; power surges on the AC line are handled by surge protective devices at the panel, not by the rod alone.
Ground rod = lightning's exit door to the earth. RF problems are solved by bonding, not by dirt.