Um, in countries where the government can play the ultimate arbiter of truth in speech they also get to determine what due process is, which usually is exactly what suits them. Private companies reflect the values of their shareholders and customers, which at least is made up of citizens without the coercive and exclusive power to say, lock you up for your reporting, or literally kill you and your loved ones over your reporting, which still happens to this day. If there is demand, and placed out of the state's hands, at least alternate channels, whether more accurate or not, more ethical or less, with or without an agenda, can exist. The alternate scenario easily renders them unable to exist in the first place. "Due process" when applied outside of official government action is simply coercing a standard set by the government upon collectives of private individuals even if - especially if - it is unwanted. It's an illusion of fairness that masks coercion, because there's either enforcement mechanisms for compliance - coercion - or there isn't - which is a charade and meaningless. Neither produces positive outcomes. Those in power will simply use it to cover up mistakes or intentional wrongdoing first.
Companies can't literally speak as in vocalize as a person, but they can, as entities, create the equivalence of speech in the societal sense, and shifting the arbiter of truth to the state will simply centralize that power in an entity that, in addition to dominating the marketplace by default - you can't exactly pick where you're born, nor where you can move to realistically for the most part - they can bring real consequences. Deplatforming is child's play compared to actual imprisonment or getting pushed out of an airborne helicopter.