slightly related... cut & pasted this from TMF about the history of carpet cleaning and how it relates to the myth of carpets resoling after cleaning.
Actually this myth has its roots in the real world. Before wall to wall (broadloom) carpet was being installed in homes, everyone had rugs. These rugs were picked up and brought in plant to be shampooed. The shampoos of the day were coconut-oil based for good foaming and a nice glossy look. The rugs were then rinsed off with garden hoses, hung to dry then returned to the consumer.
When carpet began to be installed the cleaning industry had not been upgraded to chemicals that were designed to be used in home. We were still using the same shampoos and because they were not thoroughly rinsed they left a residue behind that caused rapid resoiling. Unfortunately we still have old installers who tell customers "do not clean until you really have to because it will get dirty faster."
While the other reasons stated above are also part of the cause the legend began back 50 years ago. This is also the reason we do not use the term soaps when discussing cleaning.