There are countless reasons why, but the primary reason is that the digital world moves fast. Technology, especially software and search algorithms, are changing daily. Major and minor updates can penalize your site, and cause you to lose massive amounts of money at the drop of a hat. A site that is easy to keep up to date, and user-friendly will give a competitive edge in business. That edge directly translates to your bottom line and overall quality of life.
"All this technology is supposed to bring people together, but so many elderly people can't get to grips with it." If your target demographic is the elderly or retirees - keep in mind the reverse psychology of aging.