The answer goes back to the days of early printing.
All books and newspapers were put together by hand and the 'Print Setter' was an extremely important job.
Not only did he have to be well educated he had to be able to spell and do it all at speed.
If you think about it, to set up a line of print you have to set it up backwards so as to create a mirror image on the page.
Look at the lower case letters p and q now imagine them backwards.