On top of that, plenty of marketers are absolutely clueless about how to go about their strategy, mostly because unlike previous generations (in online ads), they don't grok the underlying tech at all.
If that's all there is to it, I expect there's a lot of needless work being done under the covers.
Although for me, it's a 50/50 split between topic-related and ads that appear to target a generic male audience, which is a very good guess for some topics.
Advertising is throwing darts at the board with your eyes closed, whenever it lands somewhere on the board and nets you point is good enough for most.
Typical conversion rates are under the 1% threshold so you accept that a lot of your spend is not efficient but when it is, you make your money back and some, if you are any good at it.
Some podcasts use "dynamic ad insertion", where the ads are inserted when you download the podcast rather than when the podcast file is created and uploaded. [0] Discovered my podcasts were tracking me when I traveled and then heard ads for an out-of-state regional chain after I returned home, clearly because I had downloaded the episodes while traveling. Overcast added privacy & tracking info, to show whether each podcast uses dynamic ad insertion or (possibly) tracks IP etc. [1].
[0] https://themarkup.org/ask-the-markup/2020/10/08/podcast-priv... [1] https://9to5mac.com/2020/09/03/podcast-privacy-alerts/