Maybe because some people are not 'professionals' and do not consider photography or life in general as a money making machine. Spending time in foreign places is an experience, a lifetime experience. The people who produced the book have been there and done that. This is what matters, not a few thousand dollars more or less for a book.
There are probably quite a few more efficient ways to earn money than beiing a photographer. Yet some people choose this activity as a job...
Umm... is that statement circular or simply linear?
Ciao - Rob C