Lack of access to health care is one reason. There are people with HIV/AIDS in many countries, including the United States, who are unable to afford medical care and medications. Without proper treatment, HIV will more than likely progress to AIDS. Also, people with HIV who are not showing symptoms and have not been tested may spread the virus to their sexual partners or introduce it into the blood supply of a community. Many places in the world do not have organizations that provide guidance and assistance on preventing and managing HIV/AIDS.
Laws against homosexuality promote fear in people who would otherwise be tested for the disease. The assertion by many that HIV/AIDS is a disease exclusively of homosexuals make anyone who tests positive a target for legal action, or worse. So people living in those cultures and under those laws do not get tested. That same misinformation leads people to not practice safe sex. After all, why protect themselves when only “the gays” have the disease?
Whether you are HIV positive or negative, prevention is everyone’s responsibility.