There is no big mystery here. Americans were dying of AIDS until big pharma dived into the problem. There have been about a dozen effective medications developed for HIV in the last 20 years. Most people diagnosed with HIV can have their viral loads lowered to near zero with a coctail of drugs and remain that way for decades.
I worked at a tertiary medical center towards the end of the AIDS epidemic. We had dozens of very sick people hospitalized waiting to die. As the meds came on line, people on deaths door started leaving the hospital through the front door rather than the morgue. Eventually, the AIDS wards were closed and the hospital went to an HIV out patient clinic. They don’t even have that anymore, HIV is treated by private doctors outside the hospital.
Most HIV positive people walk around now with undetectable viral loads. There is talk within the infectious disease profession of developing a definition of a cure so that they can start weaning a fraction of their patients completely off meds.
In Africa, it is a completely different story. The meds are too expensive and the disease is too widespread. There are various theories about why the disease affects different demographics than in the west. The one that makes the most sense to me is that there is widespread syphylis like spirochete infections that make it much easier to transmit HIV from female to male. There is a similar association with homosexual HIV transmission and syphylis in the U.S.
See my profile page.