Occasionally, Dr. Handsfield posts a little synopsis on HIV epidemiology among the general population. He posted this today and I think it is worth reading:
This is off topic for this thread, and that question has been addressed several times. But it bears repeating, since it probably is the single least understood aspect of HIV epidemiology among the general population -- certainly among most people who ask questions on this forum. So here it is again.
I only "insist" on what the data support. The epidemiology of HIV and heterosexual transmission varies widely and your premise is not universally true. In the US and most industrialized countries, there is not a "large demographic" of heterosexually infected males. In 30+ years of the HIV/AIDS epidemic in the US, only a relative handful of men (a few thousand) have acquired HIV through heterosexual exposre -- in a country with something like 120 million heterosexually active males. Further, most men infected heterosexually were the spouses or other regular partners of infected women, not infected during casual, one-time partnerships. Similarly, most heterosexually infected women in the US were the regular partners of infected men, who usually acquired their infections from injection drug use or from sex with other men. Looked at another way, there is little sustained heterosexual HIV transmission in the US and, say, Western Europe. Instead, heterosexual transmission is sporadic and uncommon, usually the result of "bridging" from more high risk populations.
The situation is very different in much of the world, especially in some (but not all) developing countries. The reasons for the differences include differing sex partner networks, background rates of circumcision and other STDs, differences in sexual practices, stage of the HIV epidemic (which translates into the proportion of infected people who have high viral loads and thus are more efficient transmitters), and numerous other factors, not fully understood.
There are exceptions; i.e., there have been and will continue to be pockets of sustained heterosexual transmission in the US, and there is continuing fear that it could become much more common -- maybe just from the bad luck of a few people transmitting infection to a few others at just the wrong time and place. But until now, that hasn't happened, and sexual behavior experts really don't see much potential for it.