Under this interpretation, being conservative is the cause of both circumcision and low hiv rates, and circumcision is negatively correlated with hiv rates.
It was, "We're going to take a chunk of individuals in Africa who engage in risky sex, and circumcise half of them, and then track how many of them end up with HIV after a few years"
If someone is engaging in risky sexual behavior, and they will continue to do so, then the 10 year span of whether or not they get HIV may be irrelevant since the disease itself is incurable and ultimately fatal because they will continue to expose themselves to the risk factor until they join the infected population.
It's also highly questionable if it would even control an epidemic in Africa effectively, seeing as how the spread is caused by misinformation in a huge part - a widespread campaign of male circumcision would likely increase the exact behavior which spreads it.