For all the horror HIV has wrought, global spending on vaccine development for HIV has been around $1 billion a year for the last few years. In contrast, the USA federal government spends $3 billion a year for HIV antiviral drugs for low-income Americans. $20,000 per patient per year for life. Unsurprisingly, new antivirals are where most of the research is.
It can sound almost like a conspiracy if I put it like that, but it's just the economics incentives. Especially since the developed countries where most of the market for charging a decent markup is, have the smallest market for most new vaccines, while having the largest markets for therapeutics for chronic conditions.
Now HIV is genuinely devillish to develop a vaccine for despite our attempts. But vaccines for hepatitis C, gonorrhea, HSV, among others appear to be possible. We almost certainly could develop effective vaccines for these with existing techniques, if someone coughed up the funding. Maybe all the buzz about mRNA vaccines will spur some progress here.