Earlier quoted context omitted.
As far as I can tell, because RSS requires the cooperation of actors who have no incentive to cooperate. If I use an RSS reader to support content, then it is under my control when I read it, if I read it, and what format to read it under. I can view the content however I'd like, and no tracking is there. All of these are unambiguously good things for me, and are anathema for the advertising industry. I cannot use RS…
I'm perfectly happy just getting headlines with links, which seems most common these days, at least for what I subscribe to. It requires I go to their site to get the content where they can (try to) shove anything they want in my face and run whatever trackers they normally do.
Once they started providing only links back to the WWW browser where everything was hard to read I gave up and now I just suffer reading in the WWW browser and frankly don't read nearly half as much online content as a result.