The difference is that private brokers don’t have “a monopoly on [legslized] violence”. Facebook doesn’t have an army of masked jack booted thugs with military gear.
Sure, but those masked thugs of yours can simply buy what they need from Facebook. They have deep pockets and it would not even be an inconvenience for them. In fact, for at least for political systems with checks and balances, subcontracting to data brokers carry huge upsides of minimizing responsibilities.