I try not to take it personally. Here is the thing, for all intensive purposes the Enclave were "Destroyed" in the West. It's word play. The people in the west saw Enclave patrols and Enclave vertibirds. They heared about them taking people. One day there was a big nuclear blast off the coast from where they came from. The Enclave remnantes pack up and leave. Now if you were a wastelander in the West and you saw the nuclear bast in the days after you notice no more patrols or any other Enclave activity but what's left moving East. What word would you use? I would use the word Destroyed.
I would say they left.
