Continuity mistake: Early in the film, as Jake and Charlie are towing a new weapon system to its destination on the Moon, we see Earth in the background, more than half illuminated by the Sun. Jake says they are 7 miles away and closing on their lunar destination (which should only take a matter of moments). A few moments later, as Jake and Charlie are still in approach, we see Earth in the background again, but it is now in a waning crescent, only 1/3 illuminated by the Sun. This would indicate over a week's passage of time.
Continuity mistake: When we first see Dr. Brakish Okun lying in bed the arm of the bed is up. Then just before he wakes up the arm is down. (00:19:45)
Chosen answer: It's technology that works, so why not use it? People still drive 20 year olds cars now, some because they like them, some because they can't afford a replacement. It wouldn't be surprising for the new technology to be very expensive or patented by the military and therefore not available for everyone.