Porn can have stories. Ultimately, it’s “romance” and not “porn” (or something else) because it’s marketed at women. Genre is a marketing tool; men are allergic to the word “romance” so something is labeled romance if aimed at women, something else if aimed at men or a general audience.
Heh, I recall a thread years ago where a woman mentioned that she and her husband had been discussing one of the Vorkosigan novels. She was amused to discover that she’d classified it as “romance with a science fiction setting”, while he’d classified it as “military sci-fi with a romance subplot. The funny part being that both were correct, it just depended on how one chose to look at it.