Why in the world?
King’s List
These cursory occurrences of the kings of Moab in the inscriptions indicate a long-standing relationship with the Neo-Assyrian Empire. Apparently a deliberate and clear distinction existed between annexed states/districts and nations that only paid tribute. The apparent policy toward subject nations was to allow the king to remain on the throne and not to interfere in internal matters as long as tribute was paid and the king appeared when called. Maintaining Ammon, Moab, and Edom as tributary states was cost effective. The obvious expenditure of military and administrative resources to form a district encouraged the Neo-Assyrians to maintain the current administration when possible.
One other Moabite king is introduced in a historical setting that portrays a growing concern alluded to in previous inscriptions. Ashurbanipal (668-633 BC) used the subject king of Moab, Kamalshaltu to defend the eastern borders of Moab against encroaching desert dwellers. These incursions of the desert dwellers upon the entire eastern fringe of Assyria's dominion brought renewed Assyrian military activity into the area. For centuries the rich Arabian trade routes had brought spices and precious goods to the north from Arabia and the seaport at Elath. Most of this trade traveled along the so-called King's Highway that traversed the steep wadis of Edom, Moab, and Ammon. Though not directly under Assyrian control, the Arabian trade route terminated in Damascus and Tyre, both of which were under the subordinating hands of the Assyrian monarch by 738 BC.