For those of us who do everything by hand, it can be tedious to implement full-text RSS feeds. It's time-consuming as it is just to update my RSS feed manually with the minimum amount of information every time I post new content. The solution of course is to automate the process but that requires a bit of skill in figuring out how to check for and parse new documents, then update the feed accordingly. Static site generators already take care of this of course but they come with other drawbacks that discourage me from using them. Just offering a different perspective on why you might occasionally find feeds that don't include the full text of the article. Some sites might be trying to drive you to their domain for clicks and ad money but some people just do everything the old school way by hand and they don't run ads or analytics anyway – the goal for them is to just inform potential readers of updates, not to force them to read content exclusively on the website.