I don't think there is one single issue that explains the rate of AIDS in Africa. From what little I have studied on disease in the third world, in general, be it AIDS or any other pandemic or fatal infectious disease, the combination of a lack of government resources or effective plan for disease management, poor access to health and social services, bankrupt and inept infrastructure, cultural myths, high price of drugs, inability of general population to have basic needs, use of rape in war, sex trafficking/slavery, and all of this further augmented by the effects of IMF restructuring, lack of education, and the biggest factor to have an effect on health and disease - poverty.
Additionally, when you reach a certain percentage of a given population infected with a disease that is in the very least debilitating, and quite often fatal, it creates a cycle where there is a tremendous impact on the economy and infrastructure, that it spirals down. When say 25% of an already poor country is too sick to work, and is dependent of social services and the government for healthcare, medication, few if any states would be able to handle it, let alone a developing nation. More people get ill, and the state is less and less able to deal with it.
http://en.wikipedia.org/wiki/AIDS#Economic_impact
Not to mention that in Africa, diseases like tuberculosis go hand in hand with AIDS, further crippling both victim and society.
And there are a myriad of other issues that feed into this as well. The manipulation of drug companies over intellectual rights of drugs through stipulations in the Tripps accord, corrupt dictators misusing funds, deceptive loans coming from the developed world, meddling by the World Bank, political unrest....... the list goes on and on.
http://www.unaids.org/en/HIV_data/2006GlobalReport/default.asp
Experts have a hard time untangling the web of precipitating factors to the AIDS epidemic in Africa. You are certainly not going to find the answer on this board. I suggest doing some reading, and laying off the conspiracy theories about big bad America as well as the racial and ill informed generalizations about promiscuous ignorant Africans.