The average doubling time IIRC for HIV is 2 years (by contrast, FYI SARS is 2 weeks, but that is another matter). This means that on average, each HIV+ person infects another person within two years. This means that (assuming a human population of 6 billion, no HIV+ genocidal policies to 'contain' the spread, no cure, the doubling rate being constant, etc.) the human race will be entirely infected within ~65 years of the first person being infected.
If you owned a pharmaceutical company, would you see the need to produce a permanent cure? People who are HIV+, if they can afford it, are permanently hooked on anti-retroviral drugs - they will pay for it or the 'withdrawal' syptoms is getting full blown AIDS sooner. Imagine the size of the market...6 billion people being hooked on your products. Imagine the profits.
If you had a permanent cure, would you release it? From the point of view of a Machiavellian CEO (I make no claim to be such a person - just speculation), someone being infected with HIV may well just be seen as 'marketing'.