It is very hard to maintain the profitability of a podcast. To get around adblockers, many podcasters have taken to editing the ads into the podcast before the podcast is uploaded to any platform. I suspect this may be the case for some of the instances you mention. These ads are not added by Spotify or any third party. The podcaster either does a sponsored ad-read or receives the audio/video for the ad from a sponsor and adds it to the podcast in post. Not much you can do at that point other than watch the cast on YouTube and use SponsorBlock.