See that’s the thing, usually the mugs that require hand washing are the cheap drop shipped crap

Mugs that are dishwasher safe are so because the manufacturer spent the extra 0.0003 cents per mug for the extra sealant layer to protect the artwork against it and tested it to ensure it can stand up to the dishwasher and started with quality materials to begin with

Those cheap crap mugs skimp out on that layer or 2, testing and use the cheapest base materials they can find