Well it looks like yours at least had stories in it

The saddest thing is that people get paid to write this.

I have a vague idea as to why it's so depressing, but my morbid curiosity craves elaboration.

Always keep in mind that everyone fucks with anthropologists. Everyone.

I once had a teacher who was doing some kind of biological research in the Amazon, and he said he often had conversations with native people about their lives that would end with them saying, "We would never tell an anthropologist this." People know when they're being observed, and people know that some of their customs and actions could be misrepresented or misunderstood by an outsider. Anthropologists are trained to get around this, but there's always someone gaming their research.

So keep your chin up; sex is probably not as "easy-access" as that book makes out.