I'm struggling to see how that is different to "rotating hero images". Is it that it doesn't rotate automatically?

What's the UX benefit here?

I get that mobile apps use horizontal swiping and some websites want to be app-like, but even in apps the only common horiztonal-swipe pattern I see is the Android hidden menus pattern, which is (a) a subject of debate in UX circles and (b) absolutely nothing like horizontally scrolling item selection, which is still a bad idea even in native mobile apps.

The other major example I can think of is Instagram's story circles, which I feel must be intentionally unusable to try and force people to view stories in their full-screen tap-to-advance format.

That's a use for sure; though it remains an anti-pattern. Don't mess with the scroll.