Take Some Fat, Any Type of Fat
And place it into a pan of cold water, and you will see it mainly sits sitting.
Now place the pan on the range and setting the heat to low, watch what happens as the water temperature gradually increases.
Much of what soils laundry,especially items worn close to the skin have body oils as the main type of "dirt". Such dirt will not shift easily in cool or cold water, hence the increased detergent action required and or enzymes.
The other problem is keeping such oily muck away from not only laundry being washed by suspension in the wash water, but also from coating the insides of a washing machine. Many European/UK washing machine repair persons are seeing an increase in washers that are full of mould, mildew and god only knows what else growing inside the machine.
Mould, contrary to popular belief just does not grow on it's own, like all living things it requires something to feed upon. In the case of gunky washing machines the residue of body oils, detergents, soaps and so forth provide the food, while the damp and warm conditions make an ideal home.