Have you read the book? It’s not trying to be an academic population-level study or anything, it’s accounts of and reflections on the reported experiences (and some verifiable—sometimes conflicting—facts surrounding those) of a few members of the Nazi party who were otherwise just ordinary people going about their lives, which is a perspective lost among focus on SS members or the Nazi political elite. A different book that was a statistical study might also be interesting, but could not accomplish the same things. It’d be a totally different book, not a better version of the same book.