Because they’re created to solve problems, fix errors, speed up your website and prevent security issues. So if you stick your head in the sand and ignore them, you’ll only get away with it for so long.
It’s like your car. If you don’t service it eventually something’s going to break, and it’ll cause more harm than if you’d caught the issue earlier, and addressed it when you had the chance. Same with your phone, or your computer. Without regular maintenance & updates the software slows down, you’re more at risk of hacking, and you’ll miss out on new and useful features too!
Website maintenance is actually business, and sales develop maintenance. It’s that important.