Administrators and Delegated users - activity not shown in Search-UnifiedAuditlog

Hi,

We use Search-UnifiedAuditlog cmdlet to retrieve "mailboxes accessed by non-owners"(EAC). Except Administrators and Delegated users activities, we can get other logs in unifiedAuditLog cmdlet. But we can able to get the logs using Search-MailboxAuditLog.  What is the reason for those logs not available in unifiedAuditLog cmdlet? Please find the attached image for reference.