Non-ballistic nuclear missiles still a purpose beyond the intertia of keeping them in service, they're the "stealth strike" option. A cruise missile is designed to hug the terrain, avoiding radar detection through proximity to ground clutter and its small radar profile which can be mistaken for an aircraft.

ICBMs are impossible to intercept once they're past the initial launch stage but they are very easy to detect which kicks off a retaliation. A cruise missile with "modern" stealth design would be an incredibly threatening weapon as you'd only need ~100 or so to cripple the retaliation capability of another nuclear power.