Podcasts nowadays tend to have way more advertising, long digressions, long intros and credit sequences, more re-runs and crossover episodes. That hasn't happened in a vaccum - the content and production values have gotten a lot more ambitious. A lot of the heavy hitters of modern podcasting have entire staffs dedicated to production, to investigation and research... they have caught up and surpassed radio shows of old, and now are more comparable in scope to a lot of documentary TV shows. Paying for all that has required a very different model of revenue, one that I'm not nearly as interested in consuming.
...but could they even support themselves with a paid subscription model? What's frustrating is that cross-promotion is very effective at increasing subscriber count.