If you publish a CMS item (for example a blog post), a publish time is set. Great for sorting blog posts by publish time, and the preferred sorting option for blogs etc.
However, if you make a change to it (for example fixing a typo) and publish the change, the old publish time is reset. This will put the blog post at the top of the site again, which is surely not intended. If you have to fix a months old blog post you don’t want it to get top spot on your home page.
Sorting by “created on” is not optimal, as you could have several blog posts in draft mode and intended to be published later - perhaps weeks later, meaning sorting your blog posts on your home page by “created on” puts them at the bottom.