And Big Tech are the one who host your account on thousands of servers versus federation where it lives on one. If that one server host gets sued or ddosed you will be unable to lose your account. Meanwhile Big Tech can withstand DDOS attacks and lawsuits.
You're mixing things up. Thousands of servers (i.e., federation) are private servers, not Big Tech servers. (Probably with some exceptions.) You can't easily sue or DDoS them all. You may not even be able to find them all.
The Big Tech single server will experience a lot more attacks, some of which it can't withstand. Related example: Apple App Store was forced to delete a hundred VPNs after the pressure of Russian government.