[naet]

I'm not 100% sure, but I think it's partly because a couple of large ad companies decided to stop backing podcasts which took a large amount of money out of the ecosystem.

Podcasts are much harder to get analytics on since the ecosystem is made up of a bunch of different podcast platforms and services, and I bet that plays into part of it. You might not be able to tell if people are downloading your podcast (a copy might be cached by a podcast provider), you might not know if people are listening or listening all the way through, if people are skipping over your ad, etc.

Ad marketers love statistics.