[catlikesshrimp]

Learning to write is difficult. You need paper and pen, and free time, and some reference, and probably a teacher

[bluGill]

Paper is easy to make from bark. Charcoal pencils are easy to find (or make) in rhe common fire. Parents can teach their children.

[unionpivo]

Paper was expensive before modern industry. Don't have reference at hand, but I remember it because I read it from few different sources.

[bluGill]

Good paper was expensive. Bark paper is easy to make and works okay. You can also write on slates and other such things.