It’s possible I am wrong, but everything I am Googling seems to say that more than 50% of new HIV transmissions are among gay men alone. Perhaps this is changing, as I would not be surprised if extremely unsafe sexual practices are becoming more common among heterosexuals - and even a small effect here would have outsized impact given the relative proportions. I would be happy to adjust my prior on this if you have some accurate demographic information you would like to link to.