How do Readers Digest benefit from their expensive prize draw marketing letters?!

How do Readers Digest benefit from their expensive prize draw marketing letters?

You know the ones, they send very elaborate envelopes with stickers and prize draw numbers, promising chance of real high value money prizes. How do they justify the expense, what's their return?

They are building up their mailing list by taking your name and address when you apply for the draw or whatever it is then later they will use your details to write to you and try to sell you their books and other stuff. It is a marketing exercise.