Admins cannot easily use event mirroring for calendar events because they cannot duplicate events. Administrators often setup series of events where they all require the same custom registration questions for the event. With cross referenced calendar events (which are no longer supported), you could copy the event in LO and all of the custom questions would copy over as part of that process. But, with event mirroring, you have to create the event in LCRM then click the mirror event button and a new LO event is generated by virtue of doing so. The event is created without any custom questions. The mirrored event functionality does not have the option to copy an event and carry over those questions, so admins are forced to do the same work over and over again.