Tasks in Crelate do not automatically sync to your mail calendar. This is by design. The intent here is that there are scenarios where it may be nice to have a notification reminder in Crelate without blocking up your mail calendar and limiting the availability that candidates/clients can book you.
If you would like an event to display on your mail calendar, that will need to be as an activity. Please see more here on: Scheduling Calendar Invites
Please note: This activity must be an Activity Mode>>Calendar Activity as noted in your "activities" section of Crelate in order to send as a calendar invitation.