The EU (more precisely France-UK-Germany, parties to the Iran nuclear deal) tried to set up a payment system to keep the deal alive, but European banks and companies like Airbus declined to participate because of the threat of US sanctions. Chinese banks are much less likely to view such sanctions as an existential risk, and many are already under sanctions anyway.

The centrality of the US also stems from its connectivity. There used to be a time when intra-European Internet traffic would be routed through the US, even though the EU economy was larger than the US’ pre Brexit.