Paul is correct, I was told by Richard Suddall of Chemspec that ph has never been a contributor in rapid resoiling.
One of the reasons I think carpets re soil is because customers treat their carpet in the same way as they did the day before they were cleaned, when a carpet is laid from new everyone takes their shoes off or avoids walking on it where as after cleaning I wonder (often know) if that because it's not a new carpet that they can still walk in with shoes on or a cuppa in hand etc, it could be a mental state of mind.
Shaun