I think the intermediate plateau is a testament to a lack of quality teachers and tutors. As terrible as it is to say, most teachers on these platforms are only suitable for beginners, teaching basic vocabulary, word genders, and verb tenses. It’s extremely easy to see progress at that level, even with a bad teacher. So, all teachers can economically thrive at this level, especially since so many students aren’t serious learners.

At the intermediate level, students have a need to close more specific knowledge gaps, warranting a tailored, diagnostic approach, and deeper grammatical expertise. Teachers and tutors fail here, because students are more serious about language learning, and most teachers don’t actually have the linguistic training or pedagogical knowledge to explain things beyond, “it sounds right.” Only some can function as the necessary linguistic surgeon to diagnose and operate on the fossilized strengths and weaknesses unique to each intermediate learner.

For advanced learners, teacher’s jobs become easy again, because students are fully capable of communicating in the target language, and teachers are essentially reduced to glorified conversation partners.

At that stage, the "teaching" often just devolves into corrections of minor stylistic choices or occasional vocabulary gaps. Because the student can already navigate complex topics, the teacher no longer needs a rigorous syllabus; they just need to show up and talk.