Mikhael, I do not know if it is a proverb or just a phrase, but I think just a phrase. The meaning of the sentence is that a person with a lot of something will always want more. If you are rich, you want to be richer. If you have many cars, you want more cars. The meaning is about the desires and wishes of people. Humans have greed and greed will always want more. However, people say it in a funny way some times (as a joke).

Another expression which communicates the same idea is this one. "The---More---the---Merrier!" It is a way of expressing disregard for moderation. An abundance of something is welcome. A little of something is disregarded as an unnecessary restraint or limitation.