I think the book was written to highlight some schools that may not get lots of attention, have an admit rate at 50% or higher, punch above their weight in giving students a solid education, and generally provide the kind of attention that turns B students into passionate learners and, ultimately accomplished in academia or the professional world. Some of the schools are better known than others. It’s become an association of sorts. Since they tend to be out of the way, they are often, as @Hapworth indicates, 10-15K cheaper than the more famous LAC in the midwest and east coast, and they often provide solid merit aid, which is a boon to middle-class “donut-hole” families that don’t have a lot saved up for college.
This list is not exhaustive. There are other, excellent, small LAC with similar characteristics.
I started a thread a while ago to broden the list: