When children learn they don’t have any scaffolding around the knowledge they are trying to build up. As adults learning a language, we do: our native language knowledge (which we built up over years of painstakingly laying brick over brick) serves as an easy shortcut to try and build more connections to the new knowledge more quickly. Fundamentally, I think we will take shortcuts when available, especially as we get less and less patient as a society.
I agree it is problematic though, and your suggested approach may be better (it’s one I attempted with Spanish, with much better results than textbook-learning and poor translations), but I bet that both you and I unknowingly “cheated” by using the scaffolding provided by our native languages. In your case, it seems your scaffolding may be more useful for Japanese. In mine, mine was much better suited for Spanish.
I doubt the status quo is going to change though. Learning a language looks much easier when the advertising makes it look like you can just use your language to gently hop across the abyss between you and your target language. [Insert obligatory Nietzsche quote]
We are understandably lazy as a whole, of course we will take the path of seemingly least resistance, so courses structured in a “quick easy progress” format are not going anywhere, even if they are not effective.