Burma's Vulnerability

What are some root causes?

The New York Times editorial sums them concisely:

[The junta's] repressive policies contributed greatly to the the disaster. Crushing poverty left many coastal communities more vulnerable to the storm than they otherwise might have been, and, as Laura Bush observed, the government-controlled news media failed to issue timely warnings. The fear now is that the generals may create obstacles to the rescue operation, which will require moving volumes of supplies as well as large numbers of aid workers, many from countries hostile to the regime.