Why are stone ware and dutch oven items exempt from bacteria?

I'm not sure what you mean by a "stoneware pan" in this case...but some pottery used for cooking shouldn't be washed with soap.

If it's glazed, then you should certainly clean it with soap, there's no reason not to.

If it's unglazed, and it's really stoneware, it should be safe to wash it with soap; since stoneware is watertight, the soap will stay on the surface, and you'll be able to rinse it off, so using soap is fine.

For water-permeable baking stones, like a pizza baking stone, or some domes used for baking bread with a french-style crisp steamed crust, then using soap is a bad idea, because you typically can't rinse the soap out afterwards. I've never tried washing one with soap, but the instructions that came with my pizza baking stone say that a soapy pizza baking stone is ruined and unusable for food.

For unglazed earthenware used for pizza, bread, or similar, you clean it with water and/or heat: if it gets dirty with something you can't wash off without soap, the remaining option is to burn it off by heating it to a high temperature in the oven, and then brushing or rinsing off the ash. This removes the "food" from derobert's list of things needed for bacteria to grow, by turing it into less nutritious ash.

The are not exempt from bacteria, and there is no reason why you should not use soap

Dutch ovens are often made from cast iron, which has then been seasoned by coating it with cooking oil, and heating until the oil polymerises into a hard coasting. Using hard set oils such as linseed make for generally better coating, but nearly any oil will do

Harsh detergents and harsh scrubbing will remove this polymer and require it to be reformed to ensure pitting and rust does not occur

The polymer layer will also reform over time by cooking with oil and high heat

Any metal pan that is heated sufficiently will not require much cleaning other than a quick wipe out to be reasonably bacteria free, but this is hardly the recommended method

Normal safe cleaning would be to use a hand wash detergent, and a cleaning cloth to remove all food and non polymerised oils from the pan

It's not special to a type of cookware. Its explained by “FAT TOM”, the things bacteria need to survive and multiple to dangerous levels: Food, Acidity, Temperature, Time, Oxygen, Moisture.

Food, proper acidity, temperature, time, and oxygen are all present. Moisture isn't.

When you clean cast iron, you typically scrub it with hot water, and often deglaze it. Deglazing it requires bringing it to sterilization temperature, so that kills anything there. Then, you drain that water out, and immediately dry it—often by throwing it back on the burner, bringing it well over the temperature required to kill pathogens.

Then you keep it dry, so nothing can start growing (no moisture).

If you instead kept the cookware damp, not only will rust form, but so will mold and bacteria.

(I'm not sure why you wouldn't use detergent on stoneware. There isn't normally a seasoning layer on that, unlike iron. I use soap on my stoneware. Sometimes I even throw it in the dishwasher.)

From the Pampered chef website:

Q: Without soap, how can my Stoneware really be clean and safe from harmful bacteria?
A: The surface of the Stoneware is virtually nonporous, so no food particles or juices can be imbedded in the Stoneware. Stoneware is safe to use as long as all food particles are removed from the surface and it is dried thoroughly before storing.