People understood binary perfectly! This was only about 50 years ago! It's a function of the electromechanical technology: It's a lot easier and more reliable

People understood binary perfectly! This was only about 50 years ago! It's a function of the electromechanical technology: It's a lot easier and more reliable to have a wheel with ten index positions on it than to have four wheels with two index positions. Many early electronic computers used binary coded decimal as a bridge between the electromechanical and the purely electronic worlds.