They’re copying the NASA model where they thinly mask their military research as science, but you’re not smart enough to see that.
ICBMs already exist. Why the fuck would they add a huge, easily spotted, immobile railroad to that.
The key advancement is supersonic. A supersonic guided missile has the potential to circumvent current (known) missile defense tools.
The space program also serves as a demonstration of capacity and deterrent. ICBMs are not launched at Cape Canaveral, but the launches there demonstrate the nation’s capabilities to the world. MAD only works if your enemies know what you can do.