The default license is always that the user grants only the site they post to the ability to host the content.
It would be nice if the default, by law, was that user created content posted publicly was available for re-hosting. Otherwise, the company would have to ensure the user understands that they are gifting the company future control in a specific way.
The result of the current climate is that these companies go against who gave them their power and because of their content arsonal are immune to reprisal.
With a default public license enforced by law, we'd see so much more innovation and cooperation of content hosts. The balance of power between content creator and platform would shift.
This would essentially solve most problems with Facebook, reddit, stackoverflow, linkedin, and more all at the same times. They'd have to try harder to do right by their users or risk losing them to a competing platform with the same data.