... at factories which were impossible to decipher.
If they simply wrote as they talked, like dictation, it would be understandable. But for whatever reason, they repeatedly struggled to do it.
I can't remember the details of their notes and memos anymore, but I'll make up an example to illustrate it. Suppose a manager wanted a machine to be shut down and thoroughly cleaned. Then their written note might be: "Machine 6 clean shut down."
Yet they had no problem expressing the instructions VERBALLY, in a completely understandable manner. So why not just write the same way?! Even if they misspelled every other word while trying to write a sentence like they talked, it would at least be much more understandable that way.