Having quality order entry software was once a rarity, and it perhaps explains why manual entry was always so prevalent. Even today, it's not always possible to find good order management software, perhaps due to software companies sticking to traditional methods.
In reality, many B2B companies are hankering for software that makes order entry easier. Your own company may still have a procedure where orders get entered manually, either in QuickBooks, or even by hand. It might sound impossible that a company would register orders on paper, though it's not entirely archaic.