New START has warhead limits, as well as missile limits, and the US has decided it'd rather allocate the warheads to bombers and SLBMs instead of ICBMs. The ICB

New START has warhead limits, as well as missile limits, and the US has decided it'd rather allocate the warheads to bombers and SLBMs instead of ICBMs. The ICBM force is in a sense, a strategic decoy: they're hardened to make you have to expend warheads on them, but the relative lack of warheads means that if you allocate more than one to take each out, you're probably not coming out ahead. But you have to honor the threat, so you can't just not hit them. So, they take 450 or more warheads from what you would otherwise want to hit.