They have already gone too long in their procrastination. The Lord has already cursed them. The curse hits them directly where they have sinned. Their pride in possessions that make them feel superior has led to their iniquities, so the Lord has cursed the ground so that it will swallow those riches. Their punishment is to lose the very thing they have sought after.
Mormon uses this prophecy as part of his connection between the events of his own day and those immediately preceding the coming of the Messiah to the New World:
Mormon 1:18-19
18 And these Gadianton robbers, who were among the Lamanites, did infest the land, insomuch that the inhabitants thereof began to hide up their treasures in the earth; and they became slippery, because the Lord had cursed the land, that they could not hold them, nor retain them again.
19 And it came to pass that there were sorceries, and witchcrafts, and magics; and the power of the evil one was wrought upon all the face of the land, even unto the fulfilling of all the words of Abinadi, and also Samuel the Lamanite.
There are three aspects of these verses that are interest. First is, of course, the fact that the “slippery earth” curse is presented at the time of Mormon. Second is that Mormon explicitly links that “slippery earth” curse to this prophecy of Samuel. The last fascinating point is that once again we see the hand of the Gadiantions in the downfall of the Nephites. For Mormon these are not coincidences, but overall patterns that declare the purposes of God.