Orbital based weapons aren't really an advantage, as it turns out. A weapon in orbit has to wait until it's over the target before it can attack, which could be a long wait. It also has all of the problems of putting anything in orbit, maintenance, station keeping, longevity, etc. In contrast, a weapon designed to fly through space on a ballistic trajectory can be much simpler and cheaper. Moreover, because they start on the Earth ICBMs can always hit their targets within a single sub-orbital hop, they don't have to wait for attack windows to line up.