Why is "Leave Page" the default button action when leaving a page with unsaved changes?

This seems to be a topic that is somewhat divided. When a page has unsaved changes I’ve seen more and more that the default action or prominent button is Leave Page instead of Continue Editing/Return etc. Facebook is one of the biggest uses of the pattern. Where does this originate? What do you think is the best primary action Leave Page or some form of Return to the page with unsaved changes?

Would the same Leave Page modal work in a similar manner for a tabbed navigation when trying to switch to another tab while a page has unsaved changes? Leave Page as the main action?

Because it’s a confirmation of the action that you have already tried to do, so you are confirming that you want to do that action. Makes sense to me?