There isn't much incentive for an author to put the effort into a comprehensive, up-to-date book on JQM development, since the development effort has stalled, and interest in JQM waned.
JQM 1.4.5 is now more than 3 years old. And jQM 1.4 was released 4 years ago.
One day, perhaps JQM 1.5 will be advanced from beta to production.
Perhaps.
Web technology in general changes quickly enough that any technical books have a brief usable lifetime. An author has to recoup their effort quickly, and then it is a constant battle to update against a moving target.
With JQM - with limited/no change in the platform, authors will have had time to catch their breath. But the underlying technology continues to progress and change, making for less and less interest and less and less practicality for JQM. It would be a very limited audience.
JQM right now is not an attractive prospect for book authors.