I think this take is not really correct, althouth it is the “modern” way RSS is used. You can have the content in the RSS feeds, and some sites do (I am pretty sure axios does this).
I think what really prevents this is the ad-driven web, and a focus on fancy web tech over more-plain text content.
Not sure why the downvotes. The RSS feed for Axios does indeed include the entire story. Check for yourself: https://api.axios.com/feed/top/
It's very convenient to have that all incorporated into your RSS reader. The only thing really stopping more sites from doing this is ad revenue.
That's a jaw-dropping misunderstanding. RSS items are not the content; they are notifications for something else. The content is elsewhere. When you have some content-object that changes, those changes appear as a train of RSS items. The RSS item is not the thing that it's about.
Your expectations and mental model are wrong, not the feed semantics.