Why are these systems not airgapped or at least run on dedicated, restricted devices and networks that only allows Epic Systems activities?!
My answer is that any rootkit or phishing schema that attempted to exfiltrate data from a client terminal would be detected by all the deeply-ingrained automated and formal procedures and systems for monitoring/auditing/alerting of access and usage of the healthcare information system. Also, depriving the doctors and nurses of Facebook/website browsing would probably be a net negative for morale, most especially in these trying times of COVID-19.