The history of book titles--that's something I'd like to know more about. Long book titles are nothing new. In bibliographies I often see historical titles that are too long to fully record. This is a really famous one from the mid-1850s:
"The history of the wars of New-England with the Eastern Indians; or, a narrative of their continued perfidy and cruelty, from the 10th of August, 1703, to the peace renewed 13th of July, 1713. And from the 25th of July, 1722, to their submission 15th December, 1725, which was ratified August 5th, 1726"
Jeez--sounds fascinating.
The titles are shaped by marketing considerations now. One thing about the current subtitling approach is that since so many books are being published annually, it's safer to make sure you have a subtitle to distinguish your book from any others that might be produced with the same title. Also, nonfiction books don't often sell in large numbers. Since with nonfiction you're often trying to reach a niche readership, the subtitle helps to telegraph to that specialized audience that the book is relevant to them. You also want to make it very clear to distributors and vendors what the book is about so they know where to shelve it, etc.
The current formula is usually "Something Catchy: Followed by a Much More Specific Description of the Book's Contents." It seems to work pretty well, even if it's aesthetically less appealing than the iconic titles of some of those older canonical works.