[nradov]

It's certainly possible to integrate directly with EHRs. Most now have pretty good implementations of the interoperability standards, at least for reading data. The problem is that to get access to that data you typically have to establish agreements with individual provider organizations, which is difficult to scale. Many provider organizations also run their own EHR instances rather than using SaaS so for those you also have to deal with all of the endpoint discovery and directory issues.

Working through aggregators such as HIEs eliminates some of those issues.