I feel this has gone over your head somewhat.
They don't care what randoms post on social media. That's not what this is about.They simply want to stop paying people to respond to the types that tweet to /post on company social media accounts. They (almost exclusively) fall into two categories:
1 - Trolls, people taking the piss and hoping for a bit of social media fame.
2 - People with a complaint who either can't be arsed to phone/email or already have, didn't like the answer they got, and are hoping the complaint being public will change things.
Having a large presence on social media isn't cheap, and they are realising/hoping it's just an huge waste of money.,