Other commenters touched on the funding side, but it's also important to remember the military distills much more concrete goals than your grandmother's applica

Other commenters touched on the funding side, but it's also important to remember the military distills much more concrete goals than your grandmother's application. 'Modest mechanical assist' is quite vague, from an engineering perspective. Especially when you have to consider that your grandmother is part of a statistical population. How far would the machine need to go? How inconvenient can it possibly be? What is your grandmother's pre-existing physical fitness level? All of these questions are very straightforward in a military application. Later moving a military-developed device to a medical-use situation is much easier when it has already been engineered for a much more specific use-case.