Same reason we do not have (health) records in the same place in a common format that would allows us to intelligently coordinate moving what supplies we do have around in a proactive fashion.
We do not have a national health care system.
We do not have a national health care system.
What makes flawless real-time communication hard is that you're talking about integrating thousands and thousands of groups of various sizes, with various technical capabilities and budgets, with various requirements, and with various legacy systems in place. You have multiple stakeholders who all want something different out of the project. You have very real security, availability, privacy, and fraud concerns. Oh and did I mention the government would really rather not pay for it?
Just creating a practical UUID for every citizen in the US is unprecedented, let alone associating all existing historical data for one person from all over the country / world with that handle, parsing that data into a standard format, and creating a system where that record could be updated in real time in a secure manner. Unsurprisingly, it's a monumental undertaking.