German cockroaches do not arrive because a kitchen is dirty. They arrive because it is warm, humid and has a water source.
We have pulled kickboards off spotless kitchens and found a full harbourage behind a dishwasher with a slow leak. Roaches need water far more urgently than food — a colony can last a month without a crumb but only a week without moisture. That is why the first thing a technician does is look for condensation, dripping traps and standing water under appliances.
Spraying surfaces is close to useless because the insects live in voids and only cross open ground at night. Gel bait placed inside those voids works because the colony carries it back. Fix the leak first, or you are treating the symptom on a schedule.