but my question is, 'does the US military use it?'. If not, why?
I'll bite, since this is something pops up, and is repeated "why don't MMAers use it, why don't <insert whatever practical ass whupping MA> use it"
Without going into the technical details, transmitting the full-blown "how" to train these skills is hard enough. I'm guessing it was really meant to be, and was transmitted in small teacher:student ratios.
It requires a lot of work on both the teacher and student. Think of it like a Professor vs. pet student. Said Prof may pick several students as being likely candidates to pursue a given subject deeper, and gives them personal instruction. The rest are given a gloss-over by-the-book version.
For most subjects, you can pick some stuff up even in the "by-the-book" version.
Unfortunately for IT, even for the average stuff, it needs to be shown hands on, in order to get your foot in the door.
Take that scenario, now imagine how the hell you'd apply it to thousands of soldiers which need to be trained. And that's not factoring in the time (at minimum 1-2 years) for the unique kind of conditioning that's trained, to kick in.
Not to say that the knowledge in IT could be used to improve some aspects of training (I've used some tricks based off of the workings of IT to obtain quick gains in some of my mma friends stand up game).
In fact the desire to short-cut some of the training and focus on short term gains is where you see a divergence in styles.
Again to clarify, IT/IS are physical skills. They use parts of the body in ways that ...well all I'll say is you have to feel it for yourself.
Being centered, balanced yatta yatta are only peripheral to the core of the matter.
FWIW Ark went to Thailand before, kicked some pads and got the comment from the Thai boxing coaches "You know we get all types...kyokushin guys etc, but they suck...but you, where the hell did you train?" (Course anyone that's been on the receiving end of Ark's kick could attest to that ^^