Didn't ads start out as integrated with content? A combination of government intervention and advertisers themselves transitioned from sponsoring a specific program with heavily integrated content (live-reads) to more polished, structured, fungible advertising of the 30-second spot.

I wouldn't be surprised if it evolves again. You already see podcasts going from sponsored live-reads to injecting ads per-download. For better or worse, this allows lower-volume (local and more targeted?) ads instead of large companies who are one of a handful of sponsors for the whole show.