Hisham Melhem outlines a major reason:
In homogeneous societies it is relatively easier for an opposition or a reform movement to articulate and agree on a set of grievances and political demands. It is more difficult to do so in heterogeneous societies, where the various groups have different pressing priorities and different visions about their society and the future. Also, it is easier for the rulers in heterogeneous countries to dilute and undermine demands for political change and reform by exploiting the various cleavages that exist in their societies.
These options were not available for former presidents Ben Ali and Mubarak.
In Lebanon, all politics is reduced to sectarianism. In Jordan, political and economic problems are viewed through the prism of Jordanian-Palestinian cleavages. In Yemen, where the population is heavily armed, political demands are undermined by the exploitation of tribal, sectarian and regional differences. In some Arab countries, significant religious and ethnic groups are disenfranchised; for example, the Shia in Saudi Arabia, Kuwait, and particularly Bahrain, where they constitute the majority; the Kurds in Syria; and the Berbers in Algeria. The legitimate grievances of these groups cannot be denied any more. In Bahrain, where the Shia majority has long complained of systematic discrimination in the political and economic spheres, calls for political and economic reforms are reduced to identity' politics or worse, and are seen by the ruling Sunni royal family and its supporters as driven by sectarian interests or outside powers'.