This is the kind of sentiment I had when people ask me about 日本語 regarding: “do Japanese people memorize all 50000+ Kanji?” I’m like “NO” since they don’t know all characters as only a small percentage of that is taught & used, around 2136. Although, some people learn jargon catered to specific fields (science, medicine) leading to them knowing 3000+ Kanji.
The estimated count for the “number of words” in English is 1,000,000 but that’s not an exact answer. The thing is, how many words is a native English speaker expected to know & understand? How much vocab do they teach students at school (from spelling to grammar)? After learning the alphabet, what types of words are taught across schools in the Anglosphere to kids?
For perspective, kids in Japan only learn 80 Kanji in their first year (mainly common & easy ones: 犬、校、九、女、男、名、森、右 to list a few) but the number expands through their years. I mean, something “similar” exists in English with spelling being taught at schools (teachers give a list of words to memorize spelling followed by a spelling test later).
The vocab lists expand from elementary to high school with difficult words (there’s a difference in difficulty with trying to spell a word like “animal” to “conscientious”). It’s like how a Japanese kid knows how to handwrite 海外 but has a hard time on trying to understand 傭兵 (ようへい) since 傭 is a harder Kanji to write in comparison to 海.
Considering its a language with thousands of years of history dating back to ancient Chinese I think at best it’s difficult to say with certainty any sort of intentionality about how kanji as a system developed, but I believe that it makes sense from an almost evolutionary standpoint that kanji simplified into groupings of radicals (which often tell a sort of story that can help to memorize that kanji) would be better remembered and passed down through generations of use. Harder kanji or ones with more unique symbols are more likely to be misremembered or simplified for ease of memorization.
But this is all speculation on my part as I’m still learning the language as it currently exists, not so much the history of written Japanese.