Its been that way for years, the ad is on the lockscreen, and its an ad for other books. The version with no advertisement is 20$ more, I don't see the problem if someone wants to get a discount for looking at ads.
Creating a different experience around reading books for those who have and those who have not is also a problem, given how important literacy and the printing press are to the development of our society.
The first or last pages of books are still frequently used to sell other books from the same author or from the same publisher. Not that long ago they'd come with cut-out cards to mail in for your order for more of the publisher's books from the partial catalog printed in your book (nobody orders by mail any more, is the only reason the stopped that, I assume). Some of my books when I was a kid would have the first chapter of another book from the same anthology series at the end, to sell it (Goosebumps did this, for example).
As much as I hate advertising, this is as good as it gets