I'll tell you why: the gold never existed, this guy is a con artist and his ploy is to pretend the government stole his gold, lose the lawsuit and claim a coverup, then raise money from people using his new "victim of the government" martyr status to make himself some sort of folk hero.
I mean come on; telling the government or anybody about the gold before you even dig it up and see for yourself? Before you even take a picture of the gold to prove it exists? Who would do that? It defies all common sense.