The MPAA is an Association.
It's a small government for studios. It's not intended to be independent, it's intended to balance power along its members.
If there was only one studio it could do ratings in-house.
It is likely that an organization like this will become a defacto standard used by all big social networks as a way to get government off their back, much like the Hayes Code and then the MPAA ratings board by the movie industry.
