Landing on an island when the whole place is terra incognita makes sense, easier to defend themselves on an island, easier to secure and keep it that way, less likely to be detected by casual passersby. The 'artifacts' described in the body of folklore about the so-called Money Pit haven't survived. This Pulitzer guy found a quincunx of stones, which is interesting, at least one of which had some kind of marks on it -- unknown script, pictographs, what it is is not clear.
Yes but why did every one (so to speak) go to the exact same island? That’s the part which is troublesome, to say the least.