2 Nephi 26
The Nephites were destroyed with great speed (it really was a matter of not many years after they rejected their last opportunity to repent). Combine that with the fact that the Lamanites were hunting them down and actively trying to destroy them and their records and we should not be surprised to find little archeological evidence of their existence and fall. Archeologists would dismiss the idea of such a complete genocide and with most of the remaining evidence being of the Lamanites that is virtually the only story they would recreate. It may well be that all the ancient American cultures identified by modern archeologists are either Jaredite or Lamanite societies.