One saving grace is that nukes do have a shelf life. They require regular maintenance too. The radioactive core of plutonium or uranium can last for a while, but the various components will degrade. I heard once on the Arms Control Wonk podcast that this could be on the order of like 10 years. Someone could still salvage that to make a dirty bomb, of course, but there’s plenty of easier ways to make a dirty bomb from other radioactive materials