Lack of books on Omaha by 2+2 writers

I have been playing hold'em for almost 2 years now and has grown a interest in pot limit omaha high. From past experience I know that 2+2 books are the best poker books available in the market today with David Sklansky as my favorite author. I know that there is a 2+2 book out about high low split by Ray Zee but pot limit omaha is one of the subject that 2+2 authors such as David Sklansky, Mason Malmuth or Ed Miller has not dedicated a entire book on. Is pot limit omaha such a unpopular game that it is not worth the investment to write a entire book on? Or is there a pot limit omaha book in the works that will be due out in the near future that I'm not aware of?