It was not happenstance that AIDS was first found in the gay community.
It was then not known outside that communuty in California.
Remember that it just presented as an upsurge in some known but previously rare dideases.
It took a long time to track down its viral cause, but it was clearly being caught, hence the A for acquired.
One early theory was that repeated exposure to sperm in the anal tract was the cause.
In the eighties it was assumed that it would spread in the heterosexual community as it did in Africa.
I remeber gravely telling my students that within ten years everyone would know personally an AIDS victim, becuse that was the current belief.
That should have happened years ago but it has not.
The reason is not clear.