The fixed missile silos out in the middle of nowhere (sorry Montana!) serve a lot of useful purposes. If you do not intend to be the one who pushes the button a

The fixed missile silos out in the middle of nowhere (sorry Montana!) serve a lot of useful purposes. If you do not intend to be the one who pushes the button and destroys the entire world, it is nice having weapons like that precisely because the adversary can see whether or not you've fired them. If the enemy can see that your ICBMs haven't launched and your bombers aren't in range to fire their cruise missiles, they know you haven't gone all the way. Additionally, silos like that are something the adversary must target if they have any hope to survive, which is one less warhead they can drop somewhere else (an air base, fleet, city, or whatever). A submarine is inherently less predictable, yes, and in terms of ratcheting down tensions that is not always great.