this was pretty bad. it was bad enough that even back then you had people pointing out how bad it was. it was so bad that various states passed laws so that it would be against the law, going forward.
the textbook's point is that even though this wasn't common place, it was somewhat taken for granted.
i can kind of understand somethings. like how it was probably far more common back then for people to be married by the ages of 15-18. i can get that. but the case of Johns and Eunice, it was shocking even then. that should tell you something.