Why does rank tracking need proxies?
Two reasons: volume and location. Search engines throttle repeated automated queries from one IP long before you finish a keyword list, and they serve different results per country and city. Proxies solve both — they spread query volume and let you query from the market you actually rank in.
Without location-accurate checks you are optimizing against results your customers never see. A US server checking google.de rankings gets neither the German index slice nor German ads.