It's one of the most common complaints we hear from office managers: the carpet looked great after the last cleaning, and a week later the hallways are gray again. This is called resoiling, and it almost always has the same cause.
When carpet is cleaned with too much detergent and not enough rinsing, sticky residue stays in the fibers. That residue grabs dirt from every pair of shoes that walks over it, so the carpet gets dirty faster than it did before it was cleaned.
Hot-water extraction solves this by pre-treating the soiled areas, then flushing the fibers with hot water and pulling the water, soil, and leftover solution back out. Done properly, the carpet is left clean and residue-free, so it stays clean longer.
For busy offices, the best results come from a schedule: vacuum every visit, spot-treat spills as they happen, and extract the main traffic lanes every few months. Carpet lasts longer, and the building looks cared for all year.