Highly produced, short run podcasts that are not tied to another property are too expensive and too risky as hits were increasingly far from guaranteed. There was only a brief window when large numbers of listeners were willing to try all of them. The last season of Serial covered some of these issues at Gimlet leading up to the Spotify sale; the rest of the market took longer to catch on, bet hard on TV license deals or simply had VC money to burn through first.
The McSweeney's author from this morning's front page article has a take: