Why:
Because expiration dates with large learner populations just create a mess on learner's portals and serve no purpose aside from disallowing them from completing that particular course. (Might be useful for phasing out a course, but the time after enrollment option feels pretty useless in an enterprise setting, without this).
The option to automatically unenroll expired enrollments would declutter learner portals and give the option for admins to have cleaner enrollment data, based on users actually actively using their courses, saving them the hassle of manually unenrolling disengaged users.
Who benefits: Users and Admins
How:
Add option to automatically unenroll expired enrollments a specific time period after the expiration date
Add a message template (and custom message option) to notify them that their course has expired. (This could exist with and without the automatic unenroll option)
I tried using the unenroll option, but it removes the whole history from their transcript. So when audited, it looks like they were never assigned the correct course (admin fault), rather than they did not complete the course (user behavior). I have a similar request along thread LMS-I-224 if you want to vote there and see if we can do something better with these expired enrollments.
I do like the idea of having an expired course have it's own message option. The way that I was able to achieve this was to allow nudge emails for a course and then set the start date to be just before it expired and just after it expired. For example in the nudge I have it nudge every 3 days with maximum of 2 nudges, then set the start date December 30th so the next one occurs January 2nd. Custom message says "Your course <<name>> has expired and will no longer be available to complete. It will remain on your dashboard, but can no longer be taken. If you feel this is an error, log onto the LMS and take a look at the course" This allows for those that are procrastinators to panic and look at their dashboard on Dec 30th for a dec 31 expiration, and then notify those who don't check that the course has expired. I hope this helps.