Not op, but markdown is much more likely to render well in different contexts, without post processing. My editor understands markdown, GitHub understands markdown, the link preview renderer in <random collaborative tool> understands markdown. It’s the lowest common denominator

That's true, and it's why we're all using it. But those different renderers all support different ill-defined interpretations of Markdown. You can forget about all of them accepting raw HTML.

It has sufficient differences to what is already accepted "everywhere" that I would have think about syntax more often than I'd like. That is enough. The minor inconveniences of Markdown incompatibilities are smaller than the inconveniece of AsciiDoc. It simply doesn't offer nearly enough potential advantages to be worth the hassle.