The market size for HIV/AIDS drugs is under $15 billion [1] so while it's not chump change, it is a tiny fraction of pharmaceutical revenue (over $900 billion I believe). Like the rest of pharma, there's a fast approaching patent cliff which will free a lot of the important IP and many nations have shown they're willing to spend billions to subsidize the development of cheaper generics so I'm not sure that this source of revenue is considered reliable by pharmaceutical companies. Cancer and HIV drugs are the most expensive to develop because they are all used in complex therapeutics and I wouldn't expect many more big blockbusters either. Note also that pharmaceutical companies acquire their IP through M&A of biotechnology startups about as often as through internal R&D and biotech VCs don't have the same incentives as the conglomerates.

Furthermore, the cost of HIV drugs isn't even the majority of the cost of HIV treatment because the constant monitoring and long term complications are extremely expensive. A single hospital visit for HIV-related pneumonia or another opportunistic infection can cost more than several years worth of the drug cocktails and the visits become more frequent and expensive with age as the weakening immune system contributes negatively to almost every other healthcare issue. The incentives for public health and universal healthcare agencies around the world is pretty cleanly aligned with curing HIV at any cost.

[1] http://store.globaldata.com/market-reports/pharmaceuticals-a...