Podcasts are following the same pattern as other media. I think it's a vicious cycle. The medium starts out with a few ads, at a higher price. Once the novelty wears off and people are used to seeing these ads, they can't fetch as much money. So the publishers start shoving more and more in, driving up the ad saturation and driving down the value (and income) from each ad.

I've been listening to podcasts since about 2010, and in that time I've witnessed podcasts that used to be ad-free jump on the Blue Apron / Stamps.com / Dollar Shave Club bandwagon. First they started with a little sponsored ad at the end of the show. Then one at the beginning. Then one commercial break. Then multiple commercial breaks. It's the same downward spiral that television went through and it's absolutely painful to watch it happen and be powerless to do anything. Maybe I should have done a better job of supporting those podcasts; I did donate to many of them. But I envision a time in the future where I'll no longer be able to feel good about listening.