But you can still hand-write any word you can spell, right? If you really try? Imagine trying to write on a whiteboard and just being completely unable to remember how to write "shoulder".
Even writing e.g. "frimaerke" is not unintelligible, though. One could also imagine that ø and æ were replaced by the more common ö and ä in the future.
I think the "there are so few letters and they are relatively simple" is the point here.
There's a big difference of degree here.