To a 1925 (99 years ago) military force, the Diego Garcia airfield would have had zero importance.
I bet that's what the UK thought about Hong Kong in the late 1800s, but when 1996 rolled around I think they (and many HKers) would have liked a longer-and-99-years lease.
While geography isn't quite destiny, it is fairly important, and having a random rock in a place where there are no other rocks will always be useful IMHO (unless we perhaps develop teleportation).
Mauritius is not China. Not that I am suggesting for this to happen, but what are they going to do if the UK just decides not to leave after 99 years?
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.