If you wanted morse code for entire messages, that would require a much larger storage ROM just to hold them. Instead of a two-byte error code holding the entire failure indication, those same two bytes now only hold maybe a word in the error message at most. And when you're troubleshooting an error, now you have to sit through the entirety of the word "Missing " after trying a fix before you can tell whether it's the same error or something different this time.

Besides, you didn't need the internet to look up the error codes when you typically had the dead-tree edition of the same information.