These are the 4 variables in cleaning a carpet.
The more time a chemical has to emulsify or encapsulate soil the higher the percentage of the soil will be transferred from carpet to chemical and removed from the carpet.
The more agitation, the more likely the chemical is to actually meet up with the soil and have a chance to emulsify or encapsulate it.
The more heat, the shorter the time it takes for emulsification and encapsulation to happen.
Similarly, very hot water can work in moderate soil situations with no chemical at all
The more chemical, the more soil that can be captured and removed with some combination of these 4 variables.
Dry methods use agitation, time and chemical in small amounts.
Extraction uses chemical, agitation and time.
Truck mounts often use only heat, but can use chemical and agitation in highly soiled situations.