In a Divi site, whenever a page or post does not have a lot of copy, i.e. when the content is short, the footer may appear to be floating in the middle of the page, leaving an awkward blank space below it.
This is especially noticeable on full width pages with no sidebar when only the footer bottom bar is used.
A truly sticky footer could be a good approach, but it would always stay there for long posts and pages too, eating up some valuable space.
So the real solution consists of using a quasi-sticky footer. Which means that it will not behave as a sticky footer all the time, but only when needed.