One thing that seem to be improving Japanese literacy across the world is Inmu gay porn meme contents. I believe it hasn't reached the US, but it is becoming eerily well known in East/Southeast Asian countries, including mainland China. It uses tiny set of vocabulary in highly repetitive manner, a la kid's picture books, but in the way relatable and addicting to social media users rather than e.g. portraying a day in the life of a cute crayon drawn caterpillar.

IMO, what that tells us is that a completely dumb repetition of small set of simple concepts to just set up the pathway can be an effective means to kickstart language acquisition process. Most language learning materials attempt to establish a compact set of rules to be expanded with a long tail of modular add-ons, even many that aims to create an alternative and less stressful approaches like Duolingo. The Inmu dictionary has less than 500 known expression, all unusable in regular communications and inappropriate in most settings, and the way it is used is simplistic, childish, disrespectful, and dumb. And I think that might be how "start with picture books" advice look like if rebuilt from first principles.