>>1052927I think that's somewhat of an overexaggeration regarding illiteracy. The thing is that Japanese has a lot of redundant kanji for elaboration in text, almost entirely done to distinguish whether or not it's a specific variation of that concept in writing - but in regular speech, you would not make that distinction because context is imminently clear about what you're talking about. Let's take a look at the following:
見る (to see) / 診る (to medically examine) / 看る (to look after, usually medical) / 観る (to watch)
And yet, they're all pronounced the same, みる and they all share the same function of looking. What about the concept of going up? Same thing, same pronunciations, different writings. How about のぼる? Same thing: 上る (to ascend, go up, etc.) / 登る (to climb up) / 騰る (to jump / suddenly go up) / 昇る (to rise). Even the on'yomi readings are a hodgepodge mixture of the same pool of terms and variations thereof. The main readings here will NEVER be forgotten. The other ones though, they can fade away in someone's mind given enough time, due to how specific and strictly literary their usage is.
It's not limited to just Japan either. Chinese is double-fucked since they don't even have a native phonetic reference system like Japanese kana and as a result, their input system is literally romanization + number to get a specific character (and that's not even touching how god awful Pinyin is at doing the job.) Over time, speakers of East Asian languages (barring South Korea) forget how to recall the character at will, even though they can read it. See:
https://en.wikipedia.org/wiki/Character_amnesia 