Yes, but advertisers (you know, Google's actual customers) don't like it, because they get less control over the appearance of their ads, and way fewer metrics/

Yes, but advertisers (you know, Google's actual customers) don't like it, because they get less control over the appearance of their ads, and way fewer metrics/information about click rates etc. It might also just be less effective than in-page advertising. Google and its peers probably know the truth of that, but I don't know if there are any reliable comparative studies in that area that don't fall into the "we tried to cram exactly the same strategy/campaign/content we would put in a banner ad into an RSS feed and got no uptick in sales" trap, but I'd love to read up on that area. Regardless, the bandwagon effect of "traditional" online advertising is such that RSS is at best an (at present) tiny new frontier that would require advertisers to re-learn or change a lot of their content strategy, and at worst an actively advertiser-hostile platform. Those are just observations; not statements of should/should-not.