I think maybe it was answered, in a way. The old guard don't have a clue why because it's totally new territory for Traveller.
It is close to a theme I used in my old Traveller games though, replacing the RTT Combat Implants with CT Combat Drug.
In my games the Imperial Army made wide use of Combat Drug. It made the troops that much more efficient with far less investment than training and equipment. The IA is a huge force in my game compared to the Imperial Marines. The IM are the cream of the recruitment crop, extensively trained, superiorly equipped, but low in numbers. The IM do not use Combat Drug because they don't need it and of course it has side effects over the long term that actually lessen the effectiveness among other problems. These long term effects wouldn't develop in a IA trooper during their effective career, usually. They would however during a IM career.
Maybe the same reason could be applied to the Combat Implants in RTT? Or maybe the designers have a better story cooked up already