Divine justice operates with precise measurement, tailoring the consequences a nation faces directly to the severity of its actions. In the case of Moab, their impending downfall involves being handed over to the people of the East [מצודת דוד]. Yet, the nature of this judgment is fundamentally different from the fate suffered by neighboring nations like Ammon.
The Ammonites actively invaded and seized parts of the Israelite inheritance, resulting in the permanent loss of their own homeland. Moab, however, committed a different offense. Their guilt lay entirely in gloating over the downfall of the Israelites. Because their actions were less severe, their punishment is similarly restricted in both time and scope, ensuring that their land will not be taken away from them forever [מלבי״ם].
Ultimately, this carefully measured disaster serves a clear purpose. Through the ruin they experience, the people of Moab will come to recognize that God is faithful to deliver appropriate and exact retribution for human behavior [מצודת דוד].