Economic reality: China needs imports of raw materials to keep the material basis of it's prosperity, manufacturing, running. So China will be forced to accept RMB payments and freezing RMB accounts means freezing itself out of resource supply chains. It is a sort of vulnerability, but creates trust.
US does not want even 0.1% vulnerability. They say they don't need to import. Ok. They have independent oil and food. Ok. Then all they really offer is paper money in exchange for everything. For them freezing accounts is costless except for the reputational hit.
Would you trust a bank that had a legal obligation to you (if they stole your money, you can sue them) or one without (if they stole your money too bad)