What was the need for Mr. Wonka to invent Vita-Wonk after the invention of Wonka Vite?

First Mr. Wonka invented Wonka-Vite potion to make people younger than their age. But something went wrong with it. After taking it may people had grown younger to an extent that their ages had gone to minus. All such people had disappeared and would be back only after they spend all those minus years being invisible. To alter those changes. Mr. Wonka decided to invent a new drug which would help people to grow older.