Why does Mr.Krab's...(spongebob)?

Mr. Krabs first opened his booming burger joint in 1977, only after discovering the secret formula of the Krabby Patty (previously known as the Quahog Burger, later known as the Barnacle Burger) and acquiring and converting the ailing Rusty Crab retirement home into a booming fast food restaurant and practically adding the K to the word rusty making it the Krusty Krab to the name.