Here is another reason behind it. I might just be making this up, but.. If it was released straight it would make it easier to OCR the documents and then put them in a digital database for easier search. If they released the actual digital records (not a copy of them) it would be easier to index skim and read.
Also, the people who are in charge of FOIA are probably not given the best, fastest and latest models of anything. FOIA grunt, "This shit has to be done by hand! It will take months to copy it all! It will cost a lot of money to do it this way!" FOIA Boss, "Exactly. Now you are beginning to understand how we can true the FOIA section into a Profit center!"