Concrete holds onto everything: tyre marks, oil drips, rust bleeding from a planter or a steel post, and the black organic film that builds on the shaded side of a building.
Different stains, different chemistry
Each of those needs its own pre treatment. Oil needs a degreaser and dwell time, rust needs an entirely different product, and organic staining needs a biocide. Plain water at high pressure lifts some of it and leaves the rest, which is why a blasted driveway can come up patchy and look worse than before it was touched.
Asphalt is not concrete
Too much pressure on asphalt strips the bitumen binder and leaves the aggregate loose underfoot, which shortens the life of the surface considerably. We drop the pressure well down and lean on chemistry instead. It takes longer and it does not chew up your driveway.