The difficulty of older games was in part because of the restrictions in place because of the technology they were using. In games today, you get hours upon hours of content and you can usually play the game over and over, playing it in a different way each time.
Even as far back as 10 years ago, it was more difficult, so one way to make a game longer and make the customer feel as if they got value for what they spent their money on was to make it harder. Sometimes they took it too far, but by making the game more challenging it made the player try over and over again, making the game longer.