The vast majority of these young women are not "AIDS hookers," they are simply the partners of men who had lots of unprotected sex with other people.
That's the thing with statistics, they're based on test results compared to the total of a population.
Any individual chance to get infected changes with each risk factor added. I totally agree with you the general chance to get infected from having one time unprotected sex is low, but any next will ad to the chance and with different partners will too.
Statistically still low but the more active you are and the more partners you have unprotected the higher the chances..
There's simply too many people in the total population that do not have unprotected sex or different partners etc to have your individual actions change the overall statistics by a lot... Yours however will increase due to your behavior.
Now for specifically the group of addicted prostitutes, i can tell you even in a country with free condoms and needles/pumps, these individuals seldom test negative on hepatitus-c, HIV, or any other STD after some time working on the streets...
And it's considered a miracle if tested negative on all of those... For the STD health department this group of street prostitutes and their clients that do not use protection is considered a high risk group, even more so than the general gay sex scene...
Now imagine a small group of people having unprotected sex with these ladies because they think only male on male anal sex results in getting HIV.... They will still hardly matter in the statistics, but what use is it for them as individual being infected?