Your website is a living thing! Well not really, it is a collection of pieces of software that work together to create what you know as your website, but it changes all the time.
Like the apps on your phone the software that makes up your website is continually developed and needs to be updated regularly. Software development is a continuous process. So just because something is ok today doesn’t mean that it will be fine tomorrow.
I'm guessing you've got better things to do than have to worry about things like website backups, security patches, server configuration and performance.