Why are SpongeBob's parents and grandmother cookies?

I know this is a dumb question, and it doesnt matter in the least, but as a mom, Im forced to have Spongebob in my life (S-Bob is like CRACK to children, I dont get it???) - anyhow, just wonderin if anyone knew why hes a sponge (also very strange, but whatever...) and his ancestors all look like chocolate chip cookies. Any one???