Couldn't you just buy a new, clean sponge....?
Not if you're a cheapskate, like some folks I know, including myself. Besides the things get groady pretty quickly under some circumstances. You'd be buying them all the time.
Doctors don't buy clean new clamps, scalpels, etc, after each surgery either, they sterilize them. Barbers used to do that with combs, scissors, and even razors. They don't do the razors anymore since HIV. At first they used a fresh disposable on each client, then in some places they just stopped giving shaves, including squaring up the sideburns and sharpening the neckline.