Hot take: there is no food safety reason to replace a sponge if it's still good at removing food from dishes. If you remove the food source, and the soap removes whatever is living on the dish, whatever is left over will die due to lack of nutrients and water. It's why in food safety courses you are taught that dishes have to dry completely. Even a sponge which has been used once will be depositing "new" pathogens onto the dish. Stuff is gonna live in the sponge. The sponge doesn't kill pathogens. Removal, soap, and desiccation do. The sponge's job is almost purely mechanical.