Then there are all the other disadvantages of orbital nukes. They can only strike on their orbital path, and only when they're in the right point of the orbit, otherwise they're very expensive to re-target because it means changing orbits. Because of all those points they're actually a lot slower to target than ICMBs. If they're in a low orbit then the orbit will decay and they will come down in a few years whether you want them to or not. If they're in a high orbit the costs are even higher and they're even slower to target. Finally, they're vulnerable to detection if they're up for any length of time. They really are a terrible idea.