Answering why Korean dropped Hanja while Japan didn't, as well as a look at the history of writing in both languages.

Sources & Further reading;
  / korean-and-japanese-particle-and-grammar-s...  

https://www.google.com/books/edition/...

https://www.joshmcneill.com/docs/Pape...

https://www.google.com/books/edition/...

https://www.jica.go.jp/jica-ri/IFIC_a...

https://www.jstor.org/stable/3096136

https://koreajoongangdaily.joins.com/...