They arent. Missiles cost millions. Rockets are cheap. Rockets are unguided. Missiles are guided. From a military perspective, spacelaunch rockets are techically "unguided" as they are not tracking a target but trying to stick to a fixed/programed trajectory. It is the seeker head that costs the millions, all the jamming/counter-jamming tech that drives up development costs.

This is a rather basic (passive) seeker head by modern standards.

https://en.wikipedia.org/wiki/File:R-27_missile_homing_head,...