One of the biggest issues regardless of design or manufacturer is that young men are not as mechanically inclined as they were in decades past.
Things as simple as changing tires, checking oil levels and basic operation of mechanical systems are alien to this generation of both civilian and military members.
If you want an OR rate, if you want crew survivability, you not only need a very basic, simple system of operation and maintenance, you really need to learn a totally new way to teach it.
When lug nuts, oil levels and checking fuel levels are a mystery to young and inexperienced operators, you've got some systems design and training challenges ahead.