Cleaning carpet, upholstery, or mattress fabric is just like washing clothes. You cannot just scale across the top with hot steam alone because that is the same as steam ironing a dirty shirt. If you steam iron a dirty shirt it may look better afterward, but if it was never washed it's still very much dirty.
In order to consider carpet or upholstery fabric clean, it must be pretreated for any existing conditions. After pretreatment dwell time it must be thoroughly rinsed, extracted, then deodorized. Cleaning detergents and spotting agents should be non-toxic, biodegradable, and safe for people and pets.