Earlier quoted context omitted.
AFAIK, the US and UK value Diego Garcia because currently there aren't geographical alternatives for that base. Where else could they put it that would have the same benefits?
There are multiple islands and archipelagos in the region. Close to Africa/ME: Maldives, Seychelles, Comoros, Mayotte Close to SE Asia: Cocos and Christmas Island Diego Garcia just happened to be forcibly depopulated by the British, so was a convenient choice.
Close to Africa/ME: Maldives, Seychelles, Comoros, Mayotte
Close to SE Asia: Cocos and Christmas Island
That's the whole point of Diego Garcia: It's not "close to" anywhere, and it's nearly in the middle of a bunch of places. That's what give it its strategic importance.