>You'd think people would learn.

Learn what? The link just goes into a long bit of semantics stemming from the author's personal dislike of how other people use "untranslatable" as a word. There's nothing to "learn" from it, because it's a nothingburger.

Meanwhile, most if not all language teaching that goes on today still does treat translation as bijection. Students are constantly asked to remember "the word for X in language Y". While that might be a good-enough approximation, it also majorly encourages the idea that that's how translation itself works - so people might be forgiven trying to set the record straight by pointing out that many words are "untranslatable" that way.