This is an important book. The authors take there best shot at answering the question they ask. The answers boil down to two parts.
The more important part is cost disease. Personal services requiring large amounts of highly skilled labor have tended to go up relative to all other things, and dentistry and college have followed a similar path. The exceptions are those services where technology has meant that fewer highly-skilled person hours are required today than in years past, e.g., stock brokers because technology means we can now do a lot of our own buying and selling.
The less important part is that college is not quite as expensive as it seems, because of the growing disparity between list price and actual price paid (less scholarships, financial aid, etc.).
One limitation of the book is that the text is very heavily explanatory, and the authors have lots to say about "Why?" and much less to say about "So what should we do about it?" and what they do have to say isn't so deeply developed or so likely to have influence. However, we must understand "Why?" before we can take any action, and this book really helps with that problem.