Is “topic-comment structure” only used for teaching second language learners Chinese?
In short, no.
As others pointed out, it started off as a tool to analyze languages and showcase their differences using topic-prominence vs subject-prominence. The main proponents being Li and Thompson.
To demonstrate the effect of topic-prominence, here are some examples:
Please let me know what else you can think of. Especially if you have non-inquisitive, non-exclamative examples.
Of course, alternatively, we can say
They are said. This ordering may convey slight different connotation. They are probably (?) much less common than topic-prominent variants.
Please supply references if you know of research measuring frequency of one vs another.
It is worth noting that the Li and Thompson paper used speech that tend not to be singular sentences as the examples of topic-prominence. e.g.
I think using single sentences is important here. In the above example, do they mean 那颗树 being topic in 那颗树叶子真大 and again for 我不喜欢 or something else?
I myself need some more examples to see this spectrum defined.
Moreover, no source discussed in this thread claims or demonstrates that topic-comment is required for explaining the syntax of Chinese sentences. Instead, I expect phrasal structure grammar to be more successful in synthesizing and predicting legible Chinese sentences. Every example above -- in my mind, I can only think of examples of topic-comment where we are just as successful in explaining (single) Chinese sentences as noun phrase + verb phrase. And if this was English the verb phrase would consist of linking verb + adjective -- requiring a linking verb. In Chinese, linking verb is optional.
Certainly sentence ordering is very flexible in Chinese relative to English. However, I don't think that the flexible ordering will break the phrasal structure approach or make it unwieldy.
All that is a discussion on how to analyze syntax. It is worth noting that Li and Thompson seems to have proposed that topic-prominence vs subject-prominence is useful in identifying the semantic of sentence as well as recognizing prevalent syntax. Languages do exhibit different preferences in what kind of sentence orders are most used. Topic- vs subject- prominence is at a minimum a prevalent concept to describe such differences.
Now onward to whether topic-comment should be taught when learning Chinese.
Well, as stated before, I fail to see how topic-comment is an exceptional structure that stands above other sentential structures in Chinese. If it is taught that way, I think it is a mistake. In using topic-comment as a standalone structure, you may as well say every sentence is topic-comment. However, it is worth highlighting a popular ordering choice in Chinese sentences. In the future, we can teach the phrasal structure of Chinese (after researchers reach a consensus, that is), and also highlight topic-comment a part of the possible structure.
A personal anecdote: before hearing about the concept, in an attempt to explain the flexible ordering that is common in Chinese sentences, I proposed this exact concept to a friend, who then told me about the topic-comment idea. So it can be useful for an illustrative purpose.
As for why topic-comment is not taught in native Chinese. Well, grammar has not been taught in Chinese schools (ie. before university; also depending on the region) since ~ early 2000. See this thread where people share their experiences. I'd like to highlight one opinion from the thread (biased selection of mine): there is not yet academic consensus of Chinese grammar. ie. No consensus phrasal structure; no consensus on which part of Chinese linguistics should be taught, which is a step beyond. Thus you cannot conclude whether topic-comment will be a productive theory to teach either.
Topic-comment structure most closely relates to the topic-prominence vs subject-prominence concept popularized by Li and Thompson. (near 1k citation)
Topic-prominence vs subject-prominence is useful in analyzing the specific preferences of a language in sentence ordering, as demonstrated by Li and Thompson.
Topic-comment is not required to explain phrasal structure in Chinese sentences. (<--- according to me. Please do propose lots of examples to test idea together.)
Due to the above, topic-comment should not be taught as a standalone grammatical structure. But is useful in showcasing popular choices of sentential ordering, ie. to showcase the topic-prominence in Chinese sentences.
The primary reason of topic-comment structure being unknown among native speakers is that mainland China has not taught grammar in school since ~ early 2000. (Example.)
Although the fact that people don't recognize this structure alludes to how it may not be a standalone structure just as I claimed.