I really don’t get how people seem to want TPRS to do things it is not designed to do, such as in a recent discussion on an email list about using TPRS to teach other areas such as history.

TPRS is used to teach language. Not facts.

Whenever you attempt to teach a body of facts using a method designed to help people acquire language, it isn’t going to work out very well. The same is true when you try to help people acquire language using a method designed to teach people a body of facts (aka traditional language teaching).
Why is it that we all recognize the latter, but not the former? We all “get” the difference between learning and acquisition, right? No one is ever going to “acquire” history.
When you insist on teaching “serious” non-fiction content using TPRS, you cut the method off at its knees. You are denying yourself much of the technique that makes TPRS work — personalization. Can you teach a non-fiction or traditional story in a closed-end way without student input? Sure you can. Will your engagement level be anything near what you’d get if the students were involved? Not usually. Kids will cooperate in many cases. But that is not making best use of the method, IMO. It makes about as much sense to me as insisting that one cannot utter a word of English in class, just because. It’s turning one’s back on a really useful tool. Your content doesn’t have to be ridiculous — talking about the kids is just as personalized and just as engaging to them as a fictional story they make up. But the common element is that THEY are driving the content, not the teacher. Imposing a story or narrative line destroys the student-centric nature of the method, IMHO.
In a case where students have enough language to really discuss a factual topic in enough detail to make that discussion worthwhile on their grade level, I doubt TPRS would be the best method to use for their language acquisition. That sounds to me like students would already have all the major structure of the language. And if there is no new structure to be acquired, there should be no circling going on, even if you are doing full-on TPRS.
If facts are taught through reading, that’s not TPRS. It’s reading. Reading is an important part of TPRS, but it’s also an important part of a lot of other methods of instruction. There are many interesting new approaches developing that include reading. That does not make those approaches TPRS.
TPRS is amazing enough for what it does extremely well — get huge amounts of language structure into heads of beginners and intermediate-level students very quickly and very accurately and in a way that lasts for a long time. That is already so much more the any other language teaching method in use today. Isn’t that enough?