The Hashemites in Transjordan had a number of advantages that their Iraqi counterpart lacked. Firstly, Transjordan's the British Mandate officials in Transjordan were generally more competent in the Transjordan and possessed a degree of local knowledge. By contrast, the British officials in Iraq were relatively ignorant of the tribal and sectarian cleavages within the Iraq. The greater administrative competence led the Mandate to make meaningful alliances with the local tribal shaykhs that would not alienate the local population. This made Transjordan much more stable than Iraq during the interwar period. Finally, Abdullah I was an extremely astute leader for the situation Transjordan found itself in. He tacked a very pragmatic course under the indirect rule of the British. He knew how to build up his mystique among the tribes and make himself essential as an intermediary between the locals and the British.
Faysal inherited in Iraq a very bad situation that he tended to make worse. He had internalized many of the anti-Shi'i biases of the Ottoman state and saw them as ignorant pawns of local shaykhs. His general strategy was to try and contain the tribes and force them to be involved in a nationalizing project. Thus there was resistance to nationalization both at the top of tribal society (the shaykhs feared losing their local power) and at the bottom (late Ottoman rule had ingrained in them a strong distrust of the central government).
sources
Alon, Yoav. The Making of Jordan Tribes, Colonialism and the Modern State. London: I.B. Tauris, 2007.
Bashkin, Orit. The Other Iraq: Pluralism and Culture in Hashemite Iraq. Stanford, Calif: Stanford University Press, 2009.