I understand the point, but I don't see how companies can be "nationalist", or think in "their country's interests". They only care about money and who knows who really control any corporation with the size that a competing social network service would require?

That's part of the point though: in most of the developed world, it is possible to know who controls a given corporation.

Because there's a rule of law, legal records, required disclosures, all subject to investigation and enforcement by an independent judiciary that creates a public record.

We can bemoan that wealthy people control a majority of assets or that some exceptions slip through the cracks at smaller scale (e.g. offshore shell companies owning assets). But by and large there's no question as to "Who owns Exxon? Or Google? Or Facebook?"

China does not have that.