What is the "default revision"?
So that means it will become the active revision shown to users. So if a revision is published its got to become the default revision as it will be shown as the page content for normal users

When you select "Archived" for a piece of content you'd want that to become the default revision too so that when users look at the page they'd see access denied. But you wouldn't have the published option ticked for "Archived"

And draft you wouldnt want to become the default revision because it's not supposed to be shown to users in that state