When is time to update your website, is your website taking forever to upload or just is not showing in search engines. Does it look dated, like the tuxedo screaming seventies that your grandfather wore for your wedding, wearing it just because it fits?
You need to remember that as technology evolves, so does the tools that are available to develop your website, per example, if you have a ten-year-old computer, it might still look good, but with the memory and speed requirements of new software it just may be frozen much more than when it was out of the box.
The same thing will happen to your website, as you are not taking advantage of new technologies that optimized your site to make it easy to find for crawlers, or to upload quickly.
Besides all the above, your website will be your company image on the internet; you need a digital storefront that looks updated and practical.