I don’t know when this started but I noticed it for the first time a few months ago. Some podcasts will have preroll ads that are obviously tailored to me since they are not in the same language as the podcast, instead they are in my native language and if I connect to a VPN in another country the ad will change to one from that country. They also seem to appear regardless of podcast app. I have used both AntennaPod and Spotify. AntennaPod is free so I guess they source their podcasts from some third party website that could be adding in the ads. But since I am paying for Spotify I am expecting not to have to listen to any ads. So who is adding in these ads? Can I get rid of them or am I just stuck with them?
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.
No that’s not it. As I mentioned in the post, these ads change based on my location. They are absolutely not added by the people making the podcast because they are not even in the same language as the rest of the podcast.