being merely cloaked, quite a few big ships should have accidently slammed into it spoiling those beautiful beaches with oil spills.

Also, if it was governmentally cloaked, then there was a time when it wasn't cloaked.
So, every little dot of an island in the Pacific (with the exception of Gilligan's Island) appears on Spain's or Britain's maps from the 16th to 19th centuries. And this one, evidently, did not.
Who was cloaking it back then?

Whatever it is, it's more than just a cloaking mechanism.