Male circumcision to fight HIV is just another myth. If you are going to be polygamous with several dozen partners at a time and not use condoms, Male circumcision is not going to make much difference.
Microtears in the foreskin are prime mechanism for transmitting the virus during heterosexual sex. (Granted polygamy is never a good idea.)
Kind of the same reason there is so much more HIV transmission in the male homosexual community. Microtears of other, shall we say, delicate tissues....