I think the main issue comes down to pressures for many different stakeholders. The large EHR vendors (like Epic) were originally designed to replace paper processes, and so they're customizable to a fault. Then, obviously, you gotta pay for the software (Epic has historically not dealt with contracts that are less than $100M, or at least that's what the rumor has always been in informatics circles), and so billing optimization gets tacked on. Issues like usability get studied regularly, but it seems like a more common topic in academic circles than in industry circles. EHRs have historically been closed systems, so you can only really make improvements if your vendor makes improvements (Epic has also, at times, contractually prohibited tools from being added on to their software) -- so, you can't rely on third parties to improve.
Silicon Valley enters the chat So, entrepreneurs see this disaster and think they can disrupt and fix the problem. Only, they know very little about the actual space. Look at the backgrounds of the founding teams of EHR startups (e.g., Practice Fusion, DrChrono) or healthcare startups with home grown EHRs (e.g., Carbon Health). There's very sparse prior healthcare experience. And, while it's totally possible to learn the space, it's hard to learn the space without repeating other's mistakes first.
So, there's been over a decade's (err, actually over 3 decades) worth of effort put in to building standards for interoperability, but the main players at the table have been the Epics... the startup scene has mostly sat it out (either because they think they can build better standards, or they're simply not aware of these efforts existing). So that just creates more tech debt, but without many of the healthcare startup CTOs realizing they've incurred more tech debt. If you've ever wondered why One Medical doesn't integrate with Apple Health, this is your answer ;)
There's a ton of really good work going on in this space though. It just gets overshadowed by 20 years of crappy user experiences with EHRs. Check out companies like Canvas Medical, or researchers like Julia Adler-Milstein or Genevieve Melton-Meaux.