I never understood the appeal of decentralized social media platforms until now. How does it make sense for large centralized platforms to police their platform

I never understood the appeal of decentralized social media platforms until now. How does it make sense for large centralized platforms to police their platform for every little thing that the current social environment finds unacceptable? People should be able to organize themselves into groups as they see fit and no unilateral decision should have final say in a global community's thoughts and discussions