Golf is hard.
Add to this the fact that most instructional golf books are not worth the paper they are printed on. Most players trying to learn how to play the game from a book have so many swing thoughts they're unable to take the club back. They stink.
Until recently, most golf instructional books were written to either help you improve your swing or trying to help golfer on the mental side of golf. The problem is that it's quite difficult to learn and build a golf swing from a book. Sure, they have pictures and illustrations, but how much can aspiring golfers learn from looking at a static picture of Tiger hitting a 300-yard drive? More importantly, how much can they teach themselves from staring at a picture of Tiger Woods?
Recently, though, the trend in instructional books seems to have shifted a little. Now you are starting to see books that help golfers from more of a statistical point of view. Recent books from Mark Broadie, Every Shot Counts, and Erik J. Barzeski and David Wedzik, Lowest Score Wins, are some examples of books that take a fresh approach using statistics to help you focus in on how to get better faster.