Looks fascinating! I can see this is a large-format book with lots of photos and they are always more expensive to produce than a standard 6x9 trade book. Just off the top of my head, I’d say he spent at least $12/copy for printing, paper, binding and shipping. Plus it has 708 pages! He’s selling the book for $45. A publisher would have to sell it for double that to make a profit.
It’s hard to say why he was turned down, but there are many reasons why a book is rejected. This could be because a similar book is already on the publisher's list, the production costs are too high vs. the number of books they can guarantee will sell, or simply because their acquisition pipeline is full. I know many publishers who will not consider a book if you can’t personally guarantee you can sell at least 5,000 copies. They want to see your mailing lists, followers, pre-sales… proof of your audience.