There wasn't really an "abandonment" - writing just evolved. Look at the difference between actual Roman writing and Carolingian Minuscule or Blackletter. Ancient Romans would have found Blackletter illegible. We can see the similarities becasue we're familiar with both.

It does seem rather drastic for just five centuries, and I probably did go a bit too far. But a society going from writing nothing by hand (the collapse is around 2100) to writing everything by hand can create some pretty drastic changes.