Our B-1s and B-52s have been redeployed Stateside (cynics might term the transfer a retrograde movement, but they’d be overstating the case) from RAF Fairford after the recent intercepted terrorist attack attempt.
My own not very humble take on that is this. Fairford has no bunkers for protecting aircraft based there; the aircraft are just parked out in the open for anyone with a long gun to take potshots at should the notion strike. The UK government’s apparent disdain for restraining terrorist wannabes—the terrorists were out on bail within hours of their arrests—emphasizes that exposure. Our bombers had no business being there for any reason other than a maintenance problem that prevented an individual bomber from reaching a serious air base.
Diego Garcia, on the other hand, is the same distance from Tehran as is Fairford. It has the same lack of bunkers, but it’s much harder for terrorists to approach.
Deployment to Diego Garcia has an additional benefit: getting there, and back at the end of a deployment, enables a number of aerial refueling squares to be filled.