I read the book when my son was looking. Pope explains, in it, why the schools that are there, are there. It’s not only about selectivity, though uber-selective schools aren’t included.
The colleges in it are all over the country, not just any one or two regions. They are all LACs and the reason for that is clear in the book intro - teaching undergraduates is integral to the philosophy.
If you look up the book on Amazon you can read the first few pages.
https://www.amazon.com/Colleges-That-Change-Lives-Schools/dp/0143122304#reader_0143122304