Separating data and mark-up - JavaScript versus XSLT

I suspect the main reason podcasts have avoided centralisation is that listeners are generally split between Spotify, Apple Podcasts, and increasingly nowadays YouTube, with a pretty small fraction from all the other platforms combined. In particular Apple Podcasts could never have become a monopoly, because not everyone has an Apple device, but podcast creators have to support it because a lot of people do have an Apple device.

Following the zero-one-infinity rule, since podcasters have to support more than one platform they'll use a third-party hosting service who know how to publish to all the platforms at once (and how to handle listener stats for all those platforms to attract advertisers, etc), so the minor platforms can still hang on. But I think it's the duopoly of commercial platforms who have allowed the industry to take that shape.