They were brutal primitives who raised the monuments for ceremonial purposes until a shortage of resources on the island led to an orgy of self-destruction. The loss of their language really is no loss at all.
Without a doubt, Bush's fault.
They seem to have used up the wood. What is the basis for your calling them brutal, though? Other than the fact that anyone who doesn't worship Jesus must be subhuman, that is.
I'm quite sure many of our ancestors would be considered 'primitive' at some point. It's amazing enough their understanding of shipbuilding and navigation. They had to get there somehow. Perhaps an understanding of the language could explain how they got there and what the purpose was for the statues.