I have a crock pot that will generate a low boil on the "Low" setting and dries out anything that is cooked for a long period. I'm wondering if the temperature regulator is too high, but I can't know that unless I know what the temperature is supposed to be.
I, like you, assumed that a slow cooker would have a temperature regulator. I took mine apart, in a bid to find the thermostat and adjust it -- and discovered that it does not have one.
Cheap slow cookers contain an heating element which delivers a constant low heat, and all you can do is choose between two or three levels of power. It does not stop supplying that heat when the contents reach a particular temperature. It just keeps pumping that heat into your food.
This means that -- as long as less heat is lost out of the cooker walls/lid than the element is putting in, the contents will keep getting hotter until they reach boiling point, whereupon the energy will instead go into turning liquid into steam.
I don't know whether more expensive slow cookers have a proper thermostat. It would be good to know.