Insulation on the dishwasher is mostly for noise and stopping moisture or heat from damaging surrounding cabinets.

The dishwasher is using new water or heating water. It is not designed to keep the same water hot for an hour plus.

The whole back of the dishwasher is a tiny piece of plastic. Not insulated at all. Some fancy ones now put a little insulation on back.

But the idea isn’t to keep heat trapped to wash dishes, but to keep heat from being released and damaging things.