There are cruise missiles powered by ramjets that go significantly supersonic, but for the most part ballistic missiles are easier to use, longer range, and harder to intercept. The prospect of anti-air systems effective enough to pose ballistic missiles trouble in a "near-peer" non-nuclear conflict is recent. Both maneuvering-capable ramjet/scramjet cruise missiles and (the significantly easier) maneuverable hypersonic re-entry vehicles that launch ballistically, are the subject of recently fielded early models, active development & active testing because of that prospect.

Hence the term "cruise", which in every other context means not traveling especially fast.