So Alien 4 takes place 200 years after the third Alien movie. And after the 1st movie, Ripley is asleep drifting in space long enough for her young daughter to grow up & die of old age....
Ripley would then be easily over 300 years old (if you still count her as a clone).
If all this is in the right context then it seems Weyland & the military have wasted alot of time trying & failing to integrate Alien technology into their own...
We do see the failed attempts during the lab scene. But who knows when they started, while they had the Ripley's alien-mixed DNA 200 years prior, the technology to try might not have been available until recent.