Why does the Watchtower release at least one new book each year?
This practice started when Judge Rutherford was running the Watchtower.
Even back in the 1930's, when the books were being sold for about 25 cents a copy, a tremendous profit was being made just by the sheer numbers of books produced. Each edition of Rutherford's books were printed by the millions! (1,000,000 * 0.25 = $250,000, even if it took 15 cents to make and distribute each copy, that would leave a profit of $100,000)
It looks to me that a "New Book Every Year" policy was started as another way of generating cash!
If there were only a fixed number of books printed, such as Russell's six volume Studies in the Scriptures", people who had a set wouldn't have to shell out money to the Society each year. That wouldn't be cost effective. You have to have your customers keep coming back again and again to buy your product.
It is another example of the Watchtower just using its members as a way to perpetuate itself.
--VM44