ive been pondering this question this morning since i posted this. i actually wrote to the inosanto academy to try to get an answere from the source.
some ideas that come to mind....dan has taken too much crap from the jkd community about his teaching of jkd so he may have decided not to write on the subject anymore, other than magazine articles. he is very busy. i know he teaches like ten classes a week at his school, aside from the seminars he does.
and yes, maybe he does prefer to teach rather than spread too much information through books and videos. but, he was a school teacher and understands the importance of texts for learning as well.
when he started the jkd series, he came out with two books...jkd training with equipment and absorb what is useful. after the second book i think he became disenchanted with the idea of finishing or continuing the series because of the nonsense that took place, and all the crap he received from various individuals.
hopefully he will someday sit down and chronicle his knowledge into books for those of us who love to read.