For a long time Stitcher was taking public podcast feeds, adding their own advertising, and re-encoding the podcasts which reduced the audio quality and made it harder for podcasters to tell how many downloads they were getting. For iHeart it’s honestly mostly ideological for me. iHeart is what Clear Channel rebranded to and they control more of American terrestrial radio than any other company. Having listened to podcasts since 2005 I liked that they were a lot smaller scale, that they were more community oriented and diy. Yes there were networks like Maximum Fun and TWiT, but none of them were on the scale that iHeart is. There is some good stuff on their network, but like a lot of the corporations that only started getting into podcasts after Serial they have a much different view of what podcasts are and should be than I do.
They’ve never really made money through the AdSense payments though, and it’s not because of adblockers. YouTube is notorious for demonetizing videos for more or less no reason and for false DMCA claims that allow trolls to hijack AdSense from the video’s creator. Most money being made by YouTubers is being made through sponsorships or direct support through Patreon/Ko-Fi/etc