Many comments here are saying that the problem is lack of trust of the tech entities. I disagree - I think the problem is capture and rent-seeking.

Hospitals and service providers in America have no incentive to do anything that would reduce switching costs and increase the quality of care that you get if you do switch. Moreover, since this is a low-information landscape with respect to both pricing and outcomes, consumers have little way of differentiating and thus service providers also have less incentive to adopt practices that improve outcomes.

Because an EHR is not just about collecting patient history and outcome. It often includes billing, accounting, and management.

Then you have to consider multiple decades of paper records, and records from other systems. Then there's many hospital systems composed of multiple health entities (hospitals, clinics, stand-alone emergency rooms). Some hospital systems span across multiple states and each state have their own set of rules (don't forget about the federal rules as well - HIPAA).

Then when you are building out your EHR system. You have to take into consideration the aspect from the doctor. There are many specialties within medicine. An EHR record from the point of view of an emergency medicine doctor vs a radiologist is very different.

Maybe because nobody trusts any of them.

I hate to say it (because it makes me groan) but I really think a trustless blockchain based solution would work best where medical professionals/researchers require active consent before pulling your records, a trustless form of anonymization/pseudonymization is built into the platform and an immutable record of every query made and why is held forever.

"all the health records were proprietary" is, as I understand it, the description of the broad status quo. There's no standard format, and many functionally-ok versions running at thousands of different hospitals, so it's apparently nigh impossible to solve the problem. See the other comments about everyone trying this and failing...

It's honestly the sort of thing where you should have a standard created by an independent group designing a standard, which is then implemented by the government (handling storage and release of records to local providers).