Mormon has prepared us for the hardening of Nephite hearts. They had seen a miracle with Nephi, and only believed for a little while. They had seen a miracle with Samuel, but only believed for a little while. By only a couple of years later, “the people began to be more hardened in iniquity, and do more of that which was contrary to the commandments of God.”
It will continue to get worse. Beginning in the ninetieth year of the reign of the judges, the people begin to have even more signs that ought to have moved them to belief. They begin to see the signs that would indicate that “the words of the prophets began to be fulfilled.” What they will do, is find a way to ignore and dismiss those signs. That is the reason that signs are such a poor means of finding faith. They can be rationalized away.