The reason DARPA is studying this it seems is to reduce its casualty rate to research new ways to treat mental illness. If you can do that you will spend less and also keep people alive. A bunch of medical research has been created for this motivation.
ARPA created the prototype to the internet. (ARPANet). The catch of the internet is that it allowed for people to disseminate information faster than anything before. You get the good (advancement of science) and the bad (misleading people).
DARPA is in the business of moonshots. They are all about high risk / high reward.
Its more likely the stuff you don't hear about didn't work in the first place.