That's because the male "lovers" were into a lot more than heterosexual sex patterns.
Consequently, even in Africa, the primary driver behind the spread of AIDS is homosexual behavior.
I had a meeting with an AIDS prevention group from Africa once and their stance was that AIDS was being spread by rampant prostitution (the implication was that it was the hetero kind of prostitution). But given the conservative nature of the foundation I was representing, I'd put a lot more stock into the homosexuality theory than the heterosexual prostitution theory.