Why can a last-second 'Stop!' call still fail on a runway?

Answer: Reaction time is too short

Reaction time is too short ✓ — Correct! By the final seconds, one or more earlier safety layers have already failed. Even if the call is heard immediately, there may not be enough distance left for a vehicle to stop or enough time left for the aircraft to avoid the conflict. The late warning is real, but the usable window may already be gone.

Radio waves slow at night — Wrong. Radio waves do not become slower at night. The problem is not signal speed; it is that human reaction and vehicle stopping distance still take time, while the runway conflict is arriving almost immediately.

Jets erase the signal — Wrong. Jet blast is not what makes the warning ineffective here. The deeper issue is timing: once a high-speed landing aircraft and a vehicle are already too close, even a correct last-second warning may come after the safest escape options have nearly disappeared.