It is pointless and argumentative to repeatedly ask the question "why was this question closed?". No new information is obtained from asking the question. It is possible that you would gain actual knowledge if all users who voted to close would explain their reasoning, but you know that this does not happen.
My position is that the "language-specific" reason (as represented either in the "close-box" or in the help center) is too telegraphic, and does not inform users what questions are likely to be closed for that reason. That means that users have to induce a generalization from the actual examples and surrounding comments for such questions. This is actually doable, for experienced users, so the only real problem is the newbies who have minimal experience in distinguishing on-topic from off-topic.
You could reasonably argue that the three existing site-specific VTC reasons are insufficient, and should be expanded to 5 (which I believe is now possible since we are out of Beta). Observationally, "language-specific" subsumes multiple distinct reasons, and the "tree" reasons suffers from over-specificity (it's not just trees) plus a small degree of over-generality (it's not about everything that pertains to trees).
One remedy would be to replace the help-center declaration of what linguistics is, changing it from "It is the scientific study of languages" to "Linguistics is the study of language systems", except that this still needs a bit more explanation. The listed item "and more!" really needs to be deleted. The "and not about" list needs to be better articulated, especially since "language-specific" does not appear in the off-topic list.