Huh now that you mention it I remember the part abnout finding the books but I just assumed they destroyed it after they searched it one last time. Didn't they say they wiped it off the map? Even if that was literally erasing it's existence from just maps wouldn't someone have found the island by now and wondered why it's not on a map or brought it to someone's attention?
It doesn't really matter whether they destroyed the books or not afterwards as my point was that the island was still very well there. When you utterly annihilate any form of life and any sign there ever was life on a specific island in a span of a few hours, you pretty much erased its existence. This is something Robin specifically alluded on when she said that you can't see people on a map.
Though it's not directly mentioned as far as I can remember, I always was under the impression that the story of Ohara was very well known, but of course only the WG version. Namely that the demons of Ohara were vile people that wanted to destroy the world and got punished for it. Frankly the WG did exactly the same thing with Enies Lobby where they put the blame on the Strawhats. Erasing an island physically on a map is rather pointless and non-sensical as that would require that you go find every map in the world where it's pictured on while people could still end up there either way as it's still physically there. Ohara was also world-famous for its scholars, so making it appear like it never existed, is kinda difficult.
Despite its destructive nature, the Buster Call is in fact a psychological weapon. This was strongly emphasized on during the Enies Lobby arc. What's the point of wasting all those resources and manpower to destroy an island if no one knows about it? The BC is to show the world what happens to the "evil" that goes against the "justice" of the WG. For the world Ohara got what it deserved and if someone already had any kind of reason to go to a cursed island, the only thing he would find there would be a no-man's land reminiscent of World War I. Having the island still be there in fact works better than it being destroyed as it gives a stronger impact. It's pretty much a variation of sticking someone's head on a stake and display it.
