I am at a loss to explain how/why gay men are still spreading AIDS.

David — although I don’t agree with the “Never Have Anal Sex, Ever” position of the self-described “frot radicals” like Bill Weintraub, I wholly affirm one of their points: the “vanillafication” of anal sex has played an important role in explaining why gay men still spread HIV among themselves.
Most gay men, at least in contemporary anglo-american gay culture, take it for granted that anal sex isn’t at all kinky or edgy or taboo. It’s something a self-respecting gay man can talk about on a first date or even DO on a first date. If a gay man wants to “take a walk on the wild side,” he could perhaps try to talk his boyfriend into golden showers, or whips-and-handcuffs, or whatever. But anal sex isn’t “a walk on the wild side,” at least in gay male culture — it’s completely vanilla.
Imagine, as a thought experiment, how the HIV epidemic might have progressed if the vast majority of gay men accepted golden showers (for example) as completely “vanilla”, while considering anal sex to be “rather kinky” — something done only occasionally, with a very trusted partner who wants to “walk on the wild side,” but certainly not something that most guys would consider altogether normal, or discuss with casual acquaintances.
Imagine, in other words, that discourse such as “Do you like it when your boyfriend pees all over you? — Well, gosh, who doesn’t!” was socially acceptable and “vanilla” within the gay male subculture, while “Are you an anal Top or Bottom?” was heard only in whispers among hard-core fetishists in S&M bars.